JPWO2011070710A1 - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

The separator (6) is disposed between the positive electrode (4) and the negative electrode (5), and has a main layer (6A) and a plurality of thin films (6B) and (6C). Each of the plurality of thin films (6B) and (6C) has a smaller film thickness than the main layer (6A), and has an ion transmittance smaller than that of the main layer (6A). The plurality of thin films (6B) and (6C) have different ion transmittances.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, there has been a demand for driving automobiles with electric energy from the viewpoint of environmental problems, and there has been a demand for direct current for power supplies for large tools and the like. In order to satisfy these requirements, there is a demand for a small and lightweight secondary battery that can be charged quickly and discharge a large current. As a typical secondary battery satisfying such a demand, a non-aqueous electrolyte secondary battery (hereinafter sometimes simply referred to as “battery”) may be mentioned.

The nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a separator. In the positive electrode, a material that reversibly electrochemically reacts with lithium ions (positive electrode active material, lithium-containing composite oxide) is held in the positive electrode current collector (see Patent Document 1). In the negative electrode, a material capable of occluding and releasing lithium (negative electrode active material such as graphite or tin alloy) is held in the negative electrode current collector (see Patent Document 2). The separator is interposed between the positive electrode and the negative electrode, prevents a short circuit from occurring between the positive electrode and the negative electrode, and holds the electrolytic solution. In the electrolytic solution, a lithium salt (for example, LiClO ₄ or LiPF ₆ ) is dissolved in an aprotic organic solvent.

  The nonaqueous electrolyte secondary battery is manufactured according to the following method. First, each of the positive electrode and the negative electrode is formed into a thin film sheet or a foil shape, and the positive electrode and the negative electrode are laminated or wound in a spiral shape via a separator. The electrode group thus produced is housed in a battery case (may be made of metal such as iron, aluminum or stainless steel, or nickel plating or the like may be applied to the case surface) A non-aqueous electrolyte is injected into the battery case. Then, the opening part of a battery case is sealed with a cover plate. An aluminum laminate film may be used instead of the metal battery case.

Japanese Patent Laid-Open No. 11-7958 Japanese Patent Laid-Open No. 11-242955

  During the production of the nonaqueous electrolyte secondary battery, a foreign substance made of metal (hereinafter referred to as “metallic foreign substance”) may be mixed. As a typical example of a metal foreign object, a metal mixed during synthesis of a positive electrode active material or a conductive agent, or a rotating part such as a bearing or a roller in a manufacturing apparatus wears during manufacturing of a nonaqueous electrolyte secondary battery. The metal piece which generate | occur | produces by can be mentioned. Therefore, examples of the metal foreign material include iron, nickel, copper, stainless steel, and brass. These metallic foreign substances are dissolved in the non-aqueous electrolyte under the operating potential of the positive electrode to form ions, and these ions are deposited as metal on the surface of the negative electrode, for example, during charging. When the metallic foreign matter deposited on the surface of the negative electrode penetrates the separator and reaches the positive electrode, an internal short circuit occurs.

  This invention is made | formed in view of this point, The objective is to provide the nonaqueous electrolyte secondary battery with which the safety | security was ensured.

  In the nonaqueous electrolyte secondary battery according to the present invention, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte are accommodated in a battery case. The separator has a main layer and a plurality of thin films. Each of the plurality of thin films has a film thickness thinner than that of the main layer, and has an ion transmittance smaller than that of the main layer. The plurality of thin films have different ion transmittances. In such a non-aqueous electrolyte secondary battery, foreign metal ions can be prevented from passing through each thin film in the thickness direction. Therefore, it can prevent that a metal foreign material ion reaches | attains on the surface of a negative electrode.

  In the nonaqueous electrolyte secondary battery according to the present invention, it is preferable that a thin film having the smallest ion permeability among a plurality of thin films is provided on the surface of the negative electrode, and a thin film having the smallest ion permeability among the plurality of thin films. Is more preferably adhered to the surface of the negative electrode. Thereby, it can suppress that a metal foreign material ion reaches | attains on the surface of a negative electrode.

  In the non-aqueous electrolyte secondary battery according to the present invention, it is preferable that the plurality of thin films are arranged so that the ion transmittance decreases from the positive electrode toward the negative electrode. Thereby, the quantity of the foreign metal ion permeate | transmitted in the thickness direction of an electrode group can be gradually reduced as it goes to a negative electrode from a positive electrode. In such a non-aqueous electrolyte secondary battery, a thin film having the largest ion permeability among a plurality of thin films may be integrated with the main layer.

  In a preferred embodiment described below, the plurality of thin films have different hexafluoropropylene concentrations, and a thin film having a high concentration of hexafluoropropylene has a larger ion permeability than a thin film having a low concentration of hexafluoropropylene. In this case, each thin film may contain a copolymer of hexafluoropropylene and vinylidene fluoride, and the thin film having the smallest ion permeability among the plurality of thin films may be made of polyvinylidene fluoride.

  In the nonaqueous electrolyte secondary battery according to the present invention, the positive electrode only needs to have a composite oxide containing lithium, a first metal (metal other than lithium), and oxygen. X / y is preferably larger than 1.05 when the total number of moles is x [mol] and the total number of moles of the first metal in the composite oxide is y [mol]. Thereby, even when the irreversible capacity is large (capacity at the first discharge is lower than the capacity at the first charge), it is possible to suppress the occurrence of an internal short circuit due to the mixing of metal foreign objects. This effect is increased when the negative electrode has silicon, tin, or a compound containing silicon or tin.

  In the present specification, “a plurality of thin films” includes a case where the boundary between thin films cannot be confirmed. For example, when thin films having a very small thickness are stacked, it may be difficult to confirm the boundary between the thin films.

  In the present specification, the “ion permeability” can be measured, for example, according to the following method. First, an electrolyte solution (A) containing a metal salt is placed on one side with a predetermined membrane (a membrane for measuring ion permeability), and a solution (B) containing no metal salt is placed on the other side. After a predetermined time has elapsed, the salt concentration in the solution (B) is measured. Alternatively, after a predetermined time has elapsed, the ionic conductivity of the solution (B) is measured, and a previously prepared calibration curve showing the relationship between the salt concentration and the ionic conductivity is used in the solution (B). Estimate the salt concentration.

  In this specification, “ion” of “ion permeability” is a cation in the non-aqueous electrolyte, and includes not only foreign metal ions but also lithium ions.

  In the present specification, “the thin film is integral with the main layer” means that the boundary between the thin film and the main layer cannot be clearly confirmed. For example, a part of the material constituting the thin film penetrates into the main layer. That is. When the main layer and the thin film are both made of resin, the thin film may be integrated with the main layer.

  In the present specification, the “surface of the positive electrode” is a surface of both surfaces of the positive electrode facing the positive electrode and the negative electrode that transfers lithium ions, and the “surface of the negative electrode” is the negative electrode and lithium ions of both surfaces of the negative electrode. This is the surface facing the positive electrode that receives and delivers.

  The present invention can provide a non-aqueous electrolyte secondary battery in which safety is guaranteed.

FIGS. 1A to 1C are cross-sectional views illustrating a state in which a metal foreign matter is deposited on the surface of the negative electrode. FIG. 2 is a longitudinal sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of an electrode group in one embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating how the foreign metal ions move in the separator in one embodiment of the present invention. FIG. 5 is a table summarizing the results of Example 1. FIG. 6 is a table summarizing the results of Example 2. FIG. 7 is a table summarizing the results of Example 3.

  When the present inventors examined the precipitation of metal foreign matter on the surface of the negative electrode, the following was found. FIGS. 1A to 1C are cross-sectional views illustrating a state in which a metal foreign matter is deposited on the surface of the negative electrode. 1A to 1C, for convenience of explanation, the film thickness of the separator 96 is shown larger than the film thicknesses of the positive electrode 94 and the negative electrode 95, and FIGS. The relationship between the film thicknesses of the positive electrode 94, the negative electrode 95, and the separator 96 shown is different from the relationship between the film thicknesses of the positive electrode, the negative electrode, and the separator in an actual nonaqueous electrolyte secondary battery.

The metal foreign matter (X) in the positive electrode 94 (especially the positive electrode active material), the metal foreign matter generated during the production of the nonaqueous electrolyte secondary battery, or the metal foreign matter generated due to wear is under the immersion potential of the positive electrode (the immersion potential is Or an ion (X ^{n +} ) that dissolves under the operating potential of the positive electrode and moves, for example, in the separator 96 toward the surface of the negative electrode 95 during charging. At this time, when the negative electrode 95 is equal to or lower than the deposition potential of the metal foreign matter, the metal foreign matter ions are deposited on the surface of the negative electrode 95 located at the shortest distance as shown in FIG.

  After the metal foreign matter 99 is deposited on the surface of the negative electrode 95, new metal foreign matter ions are preferentially deposited on the surface of the metal foreign matter 99 as shown in FIG. Therefore, the tip of the metal foreign matter 99 approaches the positive electrode 94 and finally comes into contact with the surface of the positive electrode 94 as shown in FIG. As a result, an internal short circuit occurs.

  The present inventors have completed the present invention based on the above consideration. Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiment. Moreover, below, the same code | symbol may be attached | subjected about the same member.

  In the embodiment of the present invention, a lithium ion secondary battery is taken as a specific example as a nonaqueous electrolyte secondary battery, and the configuration thereof will be described. FIG. 2 is a longitudinal sectional view of the nonaqueous electrolyte secondary battery according to the present embodiment. FIG. 3 is a cross-sectional view of the electrode group in the present embodiment.

  As shown in FIG. 2, the nonaqueous electrolyte secondary battery according to this embodiment includes a battery case 1 made of, for example, stainless steel, and an electrode group 8 accommodated in the battery case 1. In addition, a nonaqueous electrolyte is injected into the battery case 1.

  An opening 1 a is formed on the upper surface of the battery case 1. A sealing plate 2 is caulked to the opening 1a via a gasket 3, whereby the opening 1a is sealed.

  The electrode group 8 includes a positive electrode 4, a negative electrode 5, and a separator 6, and the positive electrode 4 and the negative electrode 5 are wound around the separator 6 in a spiral shape as shown in FIG. 3. An upper insulating plate 7 a is disposed above the electrode group 8, and a lower insulating plate 7 b is disposed below the electrode group 8.

  One end of an aluminum positive electrode lead 4L is attached to the positive electrode 4, and the other end of the positive electrode lead 4L is connected to a sealing plate 2 (also serving as a positive electrode terminal). One end of a negative electrode lead 5L made of nickel is attached to the negative electrode 5, and the other end of the negative electrode lead 5L is connected to the battery case 1 (also serving as a negative electrode terminal).

As shown in FIG. 3, the positive electrode 4 has a positive electrode current collector 4A and a positive electrode mixture layer 4B. The positive electrode current collector 4A is a conductive plate-like member, and is made of, for example, aluminum. The positive electrode mixture layer 4B is provided on both surfaces of the positive electrode current collector 4A, and is bonded to a positive electrode active material (a composite oxide containing lithium and a metal other than lithium (first metal) and oxygen, for example, LiCoO ₂ ). It contains an adhesive and a conductive agent.

  As shown in FIG. 3, the negative electrode 5 includes a negative electrode current collector 5A and a negative electrode active material layer 5B. The negative electrode current collector 5A is a conductive plate-like member, and is made of, for example, copper. The negative electrode active material layer 5B is provided on both surfaces of the negative electrode current collector 5A, and may contain a graphite material and a binder. Silicon, tin, a compound containing silicon, or a compound containing tin (hereinafter referred to as “tin”) Then, it is described as “metal or a compound containing a metal”).

  The separator 6 holds a non-aqueous electrolyte, and is provided between the positive electrode 4 and the negative electrode 5 as shown in FIG. The separator 6 has a main layer 6A, a first thin film 6B, and a second thin film 6C. The main layer 6 </ b> A is provided on the surface of the positive electrode 4. The main layer 6A has a high ion permeability and a predetermined mechanical strength and insulation, and is, for example, a microporous film, a woven fabric or a non-woven fabric made of polyolefin such as polypropylene or polyethylene. The second thin film 6 </ b> C is provided on the surface of the negative electrode 5 and is preferably bonded to the surface of the negative electrode 5. The first thin film 6B is sandwiched between the main layer 6A and the second thin film 6C, is preferably integral with the main layer 6A, and is preferably bonded to the second thin film 6C.

  The electrode group 8 having such a separator 6 is produced according to any of the following methods. In the first method, the second thin film 6C and the first thin film 6B are sequentially formed on the surface of the negative electrode 5, and then the main layer 6A and the first thin film 6B formed on the surface of the positive electrode 4 are formed. Wind them after bringing them into contact with each other. In the second method, the main layer 6A, the first thin film 6B, and the second thin film 6C are sequentially formed on the surface of the positive electrode 4, and then the second thin film 6C is brought into contact with the surface of the negative electrode 5. Turn around. In the third method, the first thin film 6B and the second thin film 6C are sequentially formed on the surface of the carrier (the surface of the carrier is subjected to a release treatment) and then the main body on the surface of the positive electrode 4 The first thin film 6B is peeled off from the carrier, and the first thin film 6B and the second thin film 6C are sandwiched between the main layer 6A and the negative electrode 5, and then the film is placed between the layer 6A and the negative electrode 5. Turn.

  The separator 6 in this embodiment is further shown. The main layer 6A has a larger film thickness than each of the first thin film 6B and the second thin film 6C. The thickness of the main layer 6A is, for example, 10 μm or more and 300 μm or less, preferably 10 μm or more and 40 μm or less, more preferably 15 μm or more and 30 μm or less, and most preferably 15 μm or more and 25 μm or less. The total thickness of the first thin film 6B and the second thin film 6C is, for example, 0.01 μm or more and 20 μm or less, preferably 0.1 μm or more and 15 μm or less, and preferably 0.5 μm or more and 10 μm or less. More preferably.

  If the thickness of the main layer 6A is less than 10 μm, a sufficient amount of nonaqueous electrolyte may not be retained. In addition, contact between the positive electrode 4 and the negative electrode 5 may not be avoided, and thus an internal short circuit may occur. On the other hand, if the thickness of the main layer 6 </ b> A exceeds 300 μm, the occupation ratio of the separator 6 in the electrode group 8 becomes high, so that a sufficient amount of active material may not be filled in the battery case 1.

  If the sum of the film thickness of the first thin film 6B and the film thickness of the second thin film 6C is less than 0.01 μm, it may not be possible to prevent the occurrence of an internal short circuit due to the mixing of metal foreign matter. On the other hand, when the total thickness of the first thin film 6B and the second thin film 6C exceeds 20 μm, the occupation ratio of the first thin film 6B and the second thin film 6C in the separator 6 increases. In some cases, the function of the separator 6 may be reduced. In addition, the diffusion of lithium ions in the separator 6 may be suppressed, which may cause a decrease in battery performance.

  In other words, the sum of the thickness of the first thin film 6B and the thickness of the second thin film 6C may be 0.1% or more of the thickness of the main layer 6A, and is 0.1% or more and 20%. Or less, more preferably 0.1% or more and 10% or less. If the sum of the film thickness of the first thin film 6B and the film thickness of the second thin film 6C is less than 0.1% of the thickness of the main layer 6A, it is impossible to prevent the occurrence of an internal short circuit due to the mixing of metal foreign matter. There is a case. On the other hand, if the total thickness of the first thin film 6B and the second thin film 6C exceeds 20% of the thickness of the main layer 6A, the function of the separator 6 may be deteriorated. In addition, the diffusion of lithium ions in the separator 6 may be suppressed, which may cause a decrease in battery performance.

  Furthermore, in the separator 6 in this embodiment, the main layer 6A, the first thin film 6B, and the second thin film 6C have different ion transmittances. The main layer 6A has the maximum ion transmittance, and the ion transmittance decreases in the order of the first thin film 6B and the second thin film 6C. Thereby, it is possible to prevent the occurrence of an internal short circuit due to the mixing of metal foreign matter. Below, the separator 6 in this embodiment is further demonstrated, referring FIG. FIG. 4 is a cross-sectional view illustrating how the foreign metal ions move in the separator 6 in the present embodiment. In FIG. 4, for convenience of explanation, the thickness of the separator 6 is shown larger than the thickness of each of the positive electrode 4 and the negative electrode 5, and the relationship between the thickness of the positive electrode 4, the negative electrode 5 and the separator 6 shown in FIG. Is different from the relationship of the film thicknesses of the positive electrode 4, the negative electrode 5, and the separator 6 in an actual nonaqueous electrolyte secondary battery.

  When attention is paid to the metal foreign matter mixed in the positive electrode mixture layer 4B, the metal foreign matter is dissolved as a metal ion in the nonaqueous electrolyte under the immersion potential of the positive electrode 4 or the operating potential of the positive electrode 4, for example, charging It moves toward the negative electrode 5 inside. In the separator 6, the main layer 6 </ b> A, the first thin film 6 </ b> B, and the second thin film 6 </ b> C are arranged in order from the positive electrode 4 to the negative electrode 5. For this reason, the foreign metal ions pass through the main layer 6A and arrive at the first thin film 6B. Since the first thin film 6B has an ion transmittance lower than that of the main layer 6A, some of the foreign metal ions arriving at the first thin film 6B cannot pass through the first thin film 6B, and the first thin film 6B does not pass through the first thin film 6B. It diffuses into the thin film 6B (the foreign metal ions on the left side of FIG. 4).

  The foreign metal ions transmitted through the first thin film 6B arrive at the second thin film 6C. Since the second thin film 6C has an ion transmission rate lower than that of the first thin film 6B, it is difficult for the foreign metal ions reaching the second thin film 6C to pass through the second thin film 6C. In the thin film 6C (metal foreign ion on the right side in FIG. 4). Thereby, it is possible to delay the arrival of the metal foreign matter ions to the surface of the negative electrode 5.

  Metallic foreign matter generated during the manufacture of the nonaqueous electrolyte secondary battery or metallic foreign matter caused by wear is not necessarily mixed into the positive electrode 4 and may be mixed into the main layer 6A, for example. Regardless of the position where the metal foreign matter is mixed, the metal foreign matter ions diffuse into the first thin film 6B or the second thin film 6C. Therefore, in the present embodiment, it is possible to prevent the occurrence of an internal short circuit regardless of the cause of occurrence of the metallic foreign matter.

  Even if the metal foreign matter ions that have passed through the second thin film 6C reach the surface of the negative electrode 5, the amount of the metal foreign matter ions can be kept low. Therefore, the amount of metallic foreign matter deposited on the surface of the negative electrode 5 can be reduced. In addition, the foreign metal ions transmitted through the second thin film 6C reach the surface of the negative electrode 5 after being slightly diffused in the first thin film 6B and the second thin film 6C. Therefore, it is possible to prevent the metal foreign matter from being deposited in a direction perpendicular to the surface of the negative electrode 5. From these things, in this embodiment, even if it is a case where a metal foreign material precipitates on the surface of the negative electrode 5, generation | occurrence | production of an internal short circuit can be prevented. Since the lithium ions that control the operation of the battery are much more present in the nonaqueous electrolyte than the foreign metal ions, the influence of the diffusion suppression by the first thin film 6B and the second thin film 6C and the negative electrode 5 Less susceptible to delays in reaching The present inventors have confirmed that the nonaqueous electrolyte secondary battery according to this embodiment has no problem in the operation of the battery. Each structure of the 1st thin film 6B and the 2nd thin film 6C is further demonstrated.

  The first thin film 6B and the second thin film 6C have different ion transmittances. The first thin film 6B is preferably bonded to the surfaces of the main layer 6A and the second thin film 6C, and the second thin film 6C is preferably bonded to the surface of the negative electrode 5. From these things, the 1st thin film 6B should just contain the material which can adjust ion transmittance, and the material which has adhesiveness. The second thin film 6C may include a material capable of adjusting the ion permeability and a material having an adhesive ability, or may be made of a material having an adhesive ability.

  Examples of the material capable of adjusting the ion permeability include hexafluoropropylene (hereinafter referred to as “HFP”). HFP is superior in flexibility compared to poly (vinylidene fluoride) (hereinafter referred to as “PVDF”) and so on, so that it takes in an electrolyte and swells. Therefore, HFP is excellent in affinity with the non-aqueous electrolyte. Therefore, if the concentration of HFP in the membrane is increased, the ion permeability of the membrane can be increased. Therefore, it is sufficient that the HFP concentration in the first thin film 6B is higher than the HFP concentration in the second thin film 6C. For example, the HFP concentration in the first thin film 6B is 2% by mass or more and 30% by mass or less, and the HFP concentration in the second thin film 6C is 0% by mass or more and 20% by mass or less. If the HFP concentration in the first thin film 6B is less than 2% by mass, and if the HFP concentration in the second thin film 6C exceeds 20% by mass, the first thin film 6B and the second thin film 6C Difficult to make difference in ion permeability. On the other hand, if the HFP concentration in the first thin film 6B exceeds 30% by mass, the first thin film 6B is likely to swell the nonaqueous electrolyte. Therefore, the main layer 6A, the second thin film 6C, and the first thin film It causes a decrease in adhesive strength with 6B.

  For example, PVDF, polytetrafluoroethylene, aramid resin, polyamide, and polyimide are known as materials having adhesion ability, but it is preferable that the first thin film 6B and the second thin film 6C contain PVDF. . There are three reasons for this.

  PVDF is excellent in adhesive strength. Therefore, it is possible to prevent the first thin film 6B from being peeled off from the surface of the main layer 6A or the surface of the second thin film 6C during the production of the electrode group 8, and the second thin film 6C is the surface of the first thin film 6B. Alternatively, peeling from the surface of the negative electrode 5 can be prevented.

  PVDF is excellent in flexibility. Therefore, each of the first thin film 6B and the second thin film 6C is deformed following the expansion or contraction of the negative electrode active material. Therefore, the nonaqueous electrolyte secondary battery can be charged / discharged without lowering the performance and safety, and the cycle characteristics can be prevented from lowering. This effect is increased when a metal or a compound containing a metal is used for the negative electrode active material. This is because, when the negative electrode active material is a metal or a compound containing a metal, the amount of expansion and contraction of the negative electrode active material due to charge / discharge is larger than when the negative electrode active material is a carbon material. This is because the amount of deformation of the first thin film 6B and the second thin film 6C due to the expansion and contraction of the active material increases.

  PVDF is electrically stable in the voltage range in which the nonaqueous electrolyte secondary battery operates, and does not react with the nonaqueous electrolyte.

  In view of the above, the first thin film 6B preferably contains 2% by mass or more and 30% by mass or less of HFP and PVDF, for example, 2% by mass or more and 30% by mass or less of HFP and VDF. It only has to be united. If the 1st thin film 6B consists of this copolymer, the softness | flexibility of VDF can be improved. Accordingly, the first thin film 6B is preferably made of a copolymer of HFP and VDF in an amount of 2% by mass to 30% by mass.

  The second thin film 6C preferably contains 0 mass% or more and 20 mass% or less of HFP and PVDF, for example, a copolymer of HFP and VDF of 20 mass% or less (excluding 0 mass%). It may consist of PVDF or PVDF. If the 2nd thin film 6C consists of this copolymer, the softness | flexibility of VDF can be improved. Therefore, the second thin film 6C is preferably made of a copolymer of HFP and VDF of 20% by mass or less (excluding 0% by mass).

  The second thin film 6C will be further described. Since the second thin film 6C has less HFP than the first thin film 6B, the second thin film 6C has more adhesive material than the first thin film 6B. Therefore, since the second thin film 6C has better adhesiveness than the first thin film 6B, the first thin film 6B can be bonded to the surface of the negative electrode 5 via the second thin film 6C. As described above, the second thin film 6C has a function of adhering the first thin film 6B to the negative electrode 5 in addition to the function of making it difficult to diffuse foreign metal ions as compared with the first thin film 6B.

  As described above, in the present embodiment, the separator 6 includes the first thin film 6B and the second thin film 6C. Accordingly, the foreign metal ions are diffused into the first thin film 6B or the second thin film 6C, so that the foreign metal ions can be prevented from reaching the surface of the negative electrode 5. Even if the metal foreign matter ions reach the surface of the negative electrode 5, the metal foreign matter is deposited in a direction substantially parallel to the surface of the negative electrode 5. Therefore, it is possible to prevent the metal foreign matter from being concentrated and deposited on one place of the negative electrode 5, thereby preventing the occurrence of an internal short circuit due to the contamination of the metal foreign matter, and thus the non-aqueous electrolyte 2 having excellent safety. Next battery can be provided.

  Furthermore, in the present embodiment, the main layer 6A, the first thin film 6B, and the second thin film 6C are arranged in this order from the positive electrode 4 toward the negative electrode 5. Therefore, the foreign metal ions that have passed through the film having the highest ion permeability (main layer 6A) can be diffused into the film having the medium ion permeability (first thin film 6B). In addition, foreign metal ions that have passed through a film having a moderate ion permeability (first thin film 6B) can be diffused into the film having the lowest ion permeability (second thin film 6C). Therefore, foreign metal ions can be efficiently diffused into the first thin film 6B or the second thin film 6C.

  In the present embodiment, the first thin film 6B is bonded to the surface of the negative electrode 5 via the second thin film 6C, and is integral with the main layer 6A. Therefore, the effect that the ion transmittance decreases stepwise from the positive electrode 4 toward the negative electrode 5 can be sufficiently exhibited. Further, it is possible to prevent a decrease in manufacturing yield of the electrode group 8.

  In the present embodiment, each of the first thin film 6B and the second thin film 6C is deformed following the expansion or contraction of the negative electrode active material. Therefore, it can prevent that performance and safety fall during charge / discharge, and can prevent the fall of cycling characteristics.

  In the present embodiment, the total thickness of the first thin film 6B and the second thin film 6C is much smaller than the thickness of the main layer 6A. Therefore, in this embodiment, since lithium ion diffusion is ensured, battery performance can be ensured.

  When the separator 6 in this embodiment is used when lithium is added to the negative electrode before forming the electrode group, a great effect can be obtained. This is specifically shown below.

  The nonaqueous electrolyte secondary battery generally has a problem that the capacity at the first discharge is low (the irreversible capacity is large) compared to the capacity at the first charge. This is because an irreversible reaction such as film formation occurs in the carbon material, which is the negative electrode active material, or a metal or a compound containing a metal during the initial charge. In order to solve this problem, a technique of adding lithium to the negative electrode before forming an electrode group has been proposed (for example, Japanese Patent Application Laid-Open No. 2005-085633).

  However, when a nonaqueous electrolyte secondary battery is manufactured using the above technique, a potential difference is generated between the positive electrode and the negative electrode immediately after the nonaqueous electrolyte is injected into the battery case. Therefore, immediately after injecting the nonaqueous electrolyte into the battery case, the metal foreign matter in the positive electrode is dissolved in the nonaqueous electrolyte and deposited on the surface of the negative electrode. Therefore, compared to the case where a non-aqueous electrolyte secondary battery is manufactured without using the above technique, an internal short circuit due to the mixing of metal foreign matter is likely to occur. For example, even when the amount of mixed metal foreign matter is not so large, an internal short circuit occurs.

  However, when the separator 6 in this embodiment is used, the metal foreign matter in the positive electrode 4 is dissolved in the nonaqueous electrolyte and then diffuses into the first thin film 6B or the second thin film 6C. Can be prevented from being deposited on the surface of the negative electrode 5. Therefore, in this embodiment, even when the dissolution of the metallic foreign matter starts immediately after the nonaqueous electrolyte is injected into the battery case, it is possible to prevent the occurrence of an internal short circuit due to the contamination of the metallic foreign matter.

In order to solve the problem of large irreversible capacity, the nonaqueous electrolyte secondary battery only needs to satisfy x / y> 1.05. Here, x is the total number of moles of lithium contained in the positive electrode and the negative electrode, and y is the first metal in the positive electrode active material (for example, when the positive electrode active material is LiCoO ₂ , the first metal is Co. X and y can be obtained, for example, by ICP (inductively coupled plasma) analysis. In the positive electrode active material, the molar ratio of lithium to the first metal is usually 1: 1 to 1.02. Therefore, if x / y> 1.05 is satisfied, lithium is added to the negative electrode before the electrode group is formed.

  The problem that irreversible capacity is large can be solved, so that x / y is large. However, if x / y is too large, the amount of lithium remaining in the negative electrode 5 (lithium that does not contribute to charging / discharging) increases, and the thermal stability of the negative electrode 5 may decrease. Further, when lithium enters the negative electrode active material, the negative electrode active material expands, causing the negative electrode 5 to expand. In the state where the negative electrode 5 is expanded, the non-aqueous electrolyte input / output ability is reduced, and thus the cycle characteristics may be deteriorated. From these facts, 1.05 <x / y ≦ 1.50 is preferable, and 1.05 <x / y ≦ 1.25 is more preferable.

  As a method of adding lithium to the negative electrode before forming the electrode group, lithium may be deposited on the surface of the negative electrode active material layer 5B, or lithium may be part of the negative electrode current collector 5A or the negative electrode active material layer 5B. (For example, a lithium film is adhered to the surface of the negative electrode active material layer 5B, or the lithium film is welded to a portion of the negative electrode current collector where the negative electrode active material layer is not formed).

  Nowadays, there is a demand for higher capacity of nonaqueous electrolyte secondary batteries. In order to meet this demand, it has been proposed to use not a carbon material but a metal or a compound containing a metal as a negative electrode active material. However, when the negative electrode active material is a metal or a compound containing a metal, the irreversible capacity increases as compared with the case where the negative electrode active material is a carbon material. Therefore, the effect of preventing the occurrence of an internal short circuit due to the mixing of foreign metal is that lithium is added to the negative electrode before forming the electrode group, and the negative electrode active material is a metal or a compound containing a metal. If you become very large.

  In addition, in this embodiment, you may have the structure shown below.

  The arrangement of the main layer 6A, the first thin film 6B, and the second thin film 6C in the separator 6 is not limited to the arrangement shown in FIG. 3, and may be the arrangement shown below. In the first arrangement, the first thin film 6B is provided on the surface of the positive electrode 4, the second thin film 6C is provided on the surface of the negative electrode 5, and the main layer 6A is formed with the first thin film 6B. It is sandwiched between the second thin film 6C. However, with this arrangement, the ion permeability cannot be reduced step by step from the positive electrode 4 toward the negative electrode 5. Therefore, there may be a case where the metal foreign matter ions cannot be efficiently diffused into the first thin film 6B or the second thin film 6C.

  In the second arrangement, the first thin film 6B and the second thin film 6C are arranged opposite to each other in the arrangement shown in FIG. 3, and in the third arrangement, the first thin film 6B and the first thin film 6B are arranged in the first arrangement. The second thin film 6C is disposed opposite to each other. However, in the second and third arrangements, the first thin film 6B is provided directly on the surface of the negative electrode 5 without passing through the second thin film 6C. Therefore, the adhesive strength between the first thin film 6B and the negative electrode 5 may not be ensured.

  In the fourth arrangement, the main layer 6A is provided on the surface of the negative electrode 5, the first thin film 6B is provided on the surface of the positive electrode 4, and the second thin film 6C is connected to the main layer 6A and the first layer. Between the two thin films 6B. In the fifth arrangement, the first thin film 6B and the second thin film 6C are arranged opposite to each other in the fourth arrangement. However, in the fourth and fifth arrangements, the main layer 6A is provided on the surface of the negative electrode 5 instead of the first thin film 6B and the second thin film 6C. For this reason, metal foreign matter ions may be deposited on the surface of the negative electrode 5, and the metal foreign matter deposited on the surface of the negative electrode 5 may reach the positive electrode 4 as shown in FIG.

  From the above, the arrangement shown in FIG. 3 is preferable to the first to fifth arrangements. However, in the 1st-5th arrangement | positioning, generation | occurrence | production of the internal short circuit resulting from mixing of a metal foreign material can be prevented compared with the case where a separator does not have a 1st thin film and a 2nd thin film. Therefore, the effects in the present embodiment can be obtained to some extent even in the first to fifth arrangements.

  The separator 6 preferably has a first thin film 6B and a second thin film 6C. If the separator does not have the second thin film 6C, the metal foreign matter ions may reach the surface of the negative electrode 5, and therefore it may not be possible to prevent the occurrence of an internal short circuit due to the contamination of the metal foreign matter. Moreover, since it is difficult to adhere the first thin film 6B to the negative electrode 5 or the like, the production yield of the electrode group 8 may be reduced, and the first thin film 6B is caused by expansion and contraction of the negative electrode active material. It may peel from the negative electrode 5 or the like. Further, if the separator 6 does not have the first thin film 6B, the metal foreign matter ions may not be sufficiently diffused. For this reason, the metal foreign matter is deposited intensively at one place and short-circuited. It may cause a malfunction that leads to

  The separator 6 may have three or more thin films. In this case, it is preferable that the three or more thin films are arranged so that the ion transmittance decreases from the positive electrode 4 toward the negative electrode 5 for the reason described above. However, if the number of thin films increases too much, the occupancy rate of the thin films in the separator 6 increases, causing a decrease in the function of the separator 6. Further, if the number of thin films is increased without changing the total thickness of the thin films, the thickness of each thin film becomes very thin, so that it is difficult to form each thin film. What is necessary is just to determine the number of thin films in consideration of these. If the number of thin films is increased without changing the total thickness of the thin films, the boundary between the thin films may not be confirmed.

  When the separator 6 has two thin films, the film thickness of the first thin film 6B may be substantially the same as the film thickness of the second thin film 6C (for example, the film thickness of the first thin film 6B). May be 40% or more and 60% or less of the total thickness of the first thin film 6B and the second thin film 6C), or may be much thinner than the thickness of the second thin film 6C. It may be much thicker than the film thickness of the second thin film 6C. In any case, the effect of the present embodiment can be obtained. However, if the film thickness of the first thin film 6B is substantially the same as the film thickness of the second thin film 6C, both the effect produced by the first thin film 6B and the effect produced by the second thin film 6C can be obtained in a balanced manner. be able to. Therefore, the film thickness of the first thin film 6B is preferably substantially the same as the film thickness of the second thin film 6C.

  The electrode group 8 may be formed by laminating the positive electrode 4 and the negative electrode 5 with the separator 6 interposed therebetween.

  The nonaqueous electrolyte secondary battery may include a positive electrode current collector plate instead of the positive electrode lead 4L, and may include a negative electrode current collector plate instead of the negative electrode lead 5L. If current collection is performed using the current collector plate, the resistance during current collection can be reduced as compared with the case where current collection is performed using leads, so that the output of the nonaqueous electrolyte secondary battery can be increased.

  The nonaqueous electrolyte secondary battery may include a laminate film instead of the battery case 1. If the electrode group 8 is wrapped with a laminate film, the amount of metal foreign matter derived from the metal case can be reduced as compared with the case where the electrode group 8 is accommodated in the battery case 1 made of metal. This can contribute to the effect of preventing the occurrence of an internal short circuit due to the mixing of foreign matter.

  Below, each structure, material, and manufacturing method of the positive electrode 4 and the negative electrode 5, the structure of 6 A of main layers of the separator 6, the material of a nonaqueous electrolyte, and the manufacturing method of a nonaqueous electrolyte secondary battery are shown.

-Positive electrode-
The positive electrode current collector 4A may be made of aluminum or a conductive material mainly composed of aluminum. The positive electrode current collector 4A may be a long conductive substrate or a long foil, and may have a plurality of holes.

  The thickness of the positive electrode current collector 4A is preferably 1 μm or more and 500 μm or less, and more preferably 10 μm or more and 20 μm or less. Thereby, the positive electrode 4 can be reduced in weight while maintaining the strength of the positive electrode 4.

The positive electrode active material is a composite oxide containing lithium, a first metal, and oxygen. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiCoNiO ₂ , LiCo _1-z M _z O ₂ , LiNi _1-z M _{z O 2, LiNi 1/3 Co 1/3} Mn 1/3 O 2, LiMn 2 O 4, LiMnMO 4, a LiMePO ₄ or _Li 2 MePO ₄ F. M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Me is at least one selected from Fe, Mn, Co and Ni. z is greater than 0 and less than or equal to 1. Thus, the composite oxide includes a phosphate compound. The positive electrode active material may be one in which a part of the elements of the composite oxide is replaced with another element. The positive electrode active material may be a metal oxide, lithium oxide, or a composite oxide surface-treated with a conductive agent, and the surface treatment is, for example, a hydrophobic treatment.

  The average particle size of the positive electrode active material is preferably 5 μm or more and 20 μm or less. When the average particle diameter of the positive electrode active material is less than 5 μm, the surface area of the active material particles becomes extremely large, and therefore the amount of the binder necessary for fixing the active material in the electrode plate increases. For this reason, the amount of the positive electrode active material per electrode plate is reduced, which may cause a decrease in capacity. On the other hand, when the average particle diameter of the positive electrode active material exceeds 20 μm, streaks may occur on the surface of the slurry layer when the positive electrode mixture slurry is applied to the positive electrode current collector 4A. Therefore, the average particle size of the positive electrode active material is preferably 5 μm or more and 20 μm or less.

  Examples of the binder include PVDF, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, polyacrylic acid ethyl ester, and polyacrylic acid. Hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene butadiene rubber or carboxymethylcellulose Etc. Alternatively, the binder may be tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid and hexadiene. It is a copolymer or a mixture comprising two or more selected materials.

  Among the materials listed above, PVDF and its derivatives are chemically stable in the non-aqueous electrolyte secondary battery, and can sufficiently bind the positive electrode current collector 4A and the positive electrode active material or conductive agent, Furthermore, the positive electrode active material and the conductive agent can be sufficiently bound. Therefore, when PVDF or a derivative thereof is used as the binder, a nonaqueous electrolyte secondary battery excellent in cycle characteristics and discharge performance can be provided. In addition, since PVDF and its derivatives are inexpensive, the production cost of the nonaqueous electrolyte secondary battery can be suppressed by using PVDF or its derivatives as the binder. From the above, it is preferable to use PVDF or a derivative thereof as a binder. When PVDF is used as the binder, a positive electrode mixture slurry may be prepared using a solution in which PVDF is dissolved in N-methylpyrrolidone, and powdered PVDF is dissolved in the positive electrode mixture slurry. May be.

  The conductive agent may be, for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black (AB) or ketjen black, carbon fiber, or metal Conductive fibers such as fibers may be used, carbon fluoride may be used, metal powders such as aluminum may be used, and conductive whiskers such as zinc oxide or potassium titanate may be used. It may be a conductive metal oxide such as titanium oxide or an organic conductive material such as a phenylene derivative.

  A method for manufacturing such a positive electrode 4 will be described. First, a positive electrode mixture slurry is prepared by mixing a positive electrode active material, a binder, and a conductive agent with liquid components. At this time, the positive electrode mixture slurry only needs to contain a binder of 3.0 vol% or more and 6.0 vol% or less with respect to the positive electrode active material. Next, the obtained positive electrode mixture slurry is applied on both surfaces of the positive electrode current collector 4A and dried, and the obtained positive electrode plate is rolled. Thereby, a positive electrode having a predetermined thickness is produced.

-Negative electrode-
The negative electrode current collector 5A is preferably made of stainless steel, nickel, copper, or the like. The negative electrode current collector 5A may be a long conductive substrate or a long foil, and may have a plurality of holes.

  The thickness of the negative electrode current collector 5A is preferably 1 μm or more and 500 μm or less, and more preferably 10 μm or more and 20 μm or less. Thereby, the negative electrode 5 can be reduced in weight while maintaining the strength of the negative electrode 5.

Examples of the negative electrode active material include carbon materials, metals, metal fibers, oxides, nitrides, silicon compounds, tin compounds, and various alloy materials. The carbon material is, for example, various natural graphites, cokes, graphitized carbon, carbon fibers, spherical carbon, various artificial graphites, or amorphous carbon. The silicon compound may be SiO _x (where 0.05 <x <1.95), and a part of Si may be B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, It may be a silicon alloy substituted with at least one element selected from the group consisting of Mn, Nb, Ta, V, W, Zn, C, N and Sn, or may be a silicon solid solution. . In addition, the tin compound may be, for example, Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _x (where 0 <x <2), SnO ₂ or SnSiO ₃ . The negative electrode active material may be used alone or in combination of two or more of the materials listed above.

  A method for producing such a negative electrode 5 will be described. When a carbon material is used as the negative electrode active material, first, a negative electrode active material (carbon material) and a binder are mixed with a liquid component to prepare a negative electrode mixture slurry. Next, the obtained negative electrode mixture slurry is applied on both surfaces of the negative electrode current collector 5A and dried, and the obtained negative electrode plate is rolled. Thereby, the negative electrode 5 having a predetermined thickness is produced.

  When a metal or a compound containing a metal is used as the negative electrode active material, the negative electrode active material may be vapor-deposited on both surfaces of the negative electrode current collector 5A.

  The negative electrode 5 may be preliminarily provided with lithium for supplementing the irreversible capacity.

-Separator-
The configuration of the separator 6 is as shown in the first embodiment. The main layer 6A may have the following configuration.

  The main layer 6A may be one (insulating porous particles) in which insulating particles (for example, metal oxide or metal sulfide) are bound to each other, or a microporous thin film, a woven fabric or a nonwoven fabric made of polyolefin. You may have both with a porous insulating film. The insulating particles preferably have excellent insulating properties and are resistant to deformation even at high temperatures, and the porous insulating film is made of an insulating fine powder made of an oxide such as aluminum oxide, magnesium oxide or titanium oxide. It is preferable that it is applied on top. If a microporous thin film, a woven fabric, or a nonwoven fabric made of polyolefin is used as the main layer 6A, the main layer 6A has a shutdown function, so that the temperature increase of the nonaqueous electrolyte secondary battery can be suppressed. On the other hand, if a porous insulating film is used as the main layer 6A, the shrinkage of the main layer 6A can be prevented even when the temperature of the nonaqueous electrolyte secondary battery becomes very high (eg, 200 ° C. or higher). The occurrence of a short circuit can be prevented. What is necessary is just to select the structure of 6 A of main body layers according to the use etc. of a nonaqueous electrolyte secondary battery.

  When a microporous thin film is used as the main layer 6A, the main layer 6A may be a single layer film made of one kind of material or a composite film made of two or more kinds of materials, It may be a multilayer film in which two or more layers made of different materials are laminated.

  The main layer 6A preferably has a porosity of 30% to 70%, and more preferably has a porosity of 35% to 60%. The porosity is the ratio of the volume of the holes to the total volume of the main layer 6A.

-Non-aqueous electrolyte-
The non-aqueous electrolyte may be a liquid non-aqueous electrolyte, a gel-like non-aqueous electrolyte, or a solid non-aqueous electrolyte.

  In a liquid nonaqueous electrolyte (nonaqueous electrolyte solution, which will be described later), an electrolyte (for example, a lithium salt) is dissolved in a nonaqueous solvent.

  In the gel-like nonaqueous electrolyte, the nonaqueous electrolyte is held by the polymer material. Examples of the polymer material include PVDF, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, polyacrylate, and polyvinylidene fluoride hexafluoropropylene.

  The solid non-aqueous electrolyte includes a polymer solid electrolyte.

  Below, it shows about a non-aqueous electrolyte.

  As the non-aqueous solvent, a known non-aqueous solvent can be used, and for example, a cyclic carbonate, a chain carbonate, or a cyclic carboxylic acid ester can be used. The cyclic carbonate is, for example, propylene carbonate (PC) or ethylene carbonate (EC). The chain carbonate is, for example, diethyl carbonate (DEC), ethyl methyl carbonate (EMC) or dimethyl carbonate (DMC). The cyclic carboxylic acid ester is, for example, γ-butyrolactone (GBL; gamma-butyrolactone) or γ-valerolactone (GVL). As the non-aqueous solvent, one of the non-aqueous solvents listed above may be used alone, or two or more thereof may be used in combination.

Examples of the electrolyte include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr , LiI, chloroborane lithium, borates, or imide salts. Examples of the borate salts include bis (1,2-benzenediolate (2-)-O, O ′) lithium borate, bis (2,3-naphthalenedioleate (2-)-O, O ′) boron. Lithium acid, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, or bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) boron Lithium acid. Examples of the imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate (LiN (CF ₃ SO ₂ ) (C ₄ F ₉ ). SO _2)), or a bispentafluoroethanesulfonyl imide lithium _{((C 2 F 5 SO 2} ) 2 NLi). As the electrolyte, one of the electrolytes listed above may be used alone, or two or more may be used in combination.

The concentration of the electrolyte is preferably 0.5 mol / m ³ or more and 2 mol / m ³ or less.

  The nonaqueous electrolytic solution may contain the following additives in addition to the nonaqueous solvent and the electrolyte. This additive is decomposed on the surface of the negative electrode active material layer, whereby a film having high lithium ion conductivity is formed on the surface of the negative electrode active material layer. Therefore, the charge / discharge efficiency of the nonaqueous electrolyte secondary battery can be increased. Examples of the additive having such a function include vinylene carbonate (VC), 4-methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4-ethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, 4 -Propylene vinylene carbonate, 4,5-dipropyl vinylene carbonate, 4-phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl ethylene carbonate (VEC), or divinyl ethylene carbonate. As an additive, one of the materials listed above may be used alone, or two or more of the materials listed above may be used in combination. As an additive, it is preferable to use at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate. The additive may be one in which some of the hydrogen atoms in the materials listed above are substituted with fluorine atoms.

  The nonaqueous electrolytic solution may contain a benzene derivative in addition to the nonaqueous solvent and the electrolyte. The benzene derivative preferably has a phenyl group, and preferably has a phenyl group and a cyclic compound group bonded to positions adjacent to each other. Here, the benzene derivative is, for example, cyclohexylbenzene, biphenyl, or diphenyl ether. The cyclic compound group is, for example, a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, or a phenoxy group. As the benzene derivative, one of the materials listed above may be used alone, or two or more of the materials listed above may be used in combination. In addition, the nonaqueous solvent should just contain 10 vol% or less of benzene derivatives. If the non-aqueous electrolyte contains such a benzene derivative, during overcharge, the benzene derivative is decomposed and a film is formed on the surface of the electrode, thereby inactivating the non-aqueous electrolyte secondary battery. Can do.

  A method for manufacturing a nonaqueous electrolyte secondary battery will be described. First, the positive electrode lead 4L is connected to a portion of the positive electrode current collector 4A where the positive electrode mixture layer 4B is not provided, and the negative electrode lead 5L is connected to a portion of the negative electrode current collector 5A where the negative electrode active material layer 5B is not provided. Connect. Next, the positive electrode 4 and the negative electrode 5 are wound through the separator 6 to produce the electrode group 8. At this time, it is confirmed that the positive electrode lead 4L and the negative electrode lead 5L extend in opposite directions. Subsequently, the upper insulating plate 7 a is disposed at the upper end of the electrode group 8, and the lower insulating plate 7 b is disposed at the lower end of the electrode group 8. Then, the negative electrode lead 5 </ b> L is connected to the battery case 1, the positive electrode lead 4 </ b> L is connected to the sealing plate 2, and the electrode group 8 is accommodated in the battery case 1. Thereafter, a non-aqueous electrolyte is injected into the battery case 1 by a decompression method. Then, the opening 1 a of the battery case 1 is sealed with the sealing plate 2 via the gasket 3.

  Examples of the present invention will be described below. In addition, this invention is not limited to the Example shown below.

[Example 1]
1. Manufacturing method of non-aqueous electrolyte secondary battery (Battery 1)
-Production of positive electrode-
First, LiNi _0.82 Co _0.15 Al _0.03 O ₂ (positive electrode active material) having an average particle diameter of 10 μm was prepared.

Next, 4.5 parts by mass of acetylene black (conductive agent) and 4.7 parts by mass of PVDF (binder) are added to 100 parts by mass of LiNi _0.82 Co _0.15 Al _0.03 O _2. A solution dissolved in a solvent of N-methylpyrrolidone (NMP, NMP is an abbreviation for N-methylpyrrolidone) was mixed. As a result, a positive electrode mixture slurry was obtained.

  This positive electrode mixture slurry was applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm and dried, and the obtained electrode plate was rolled. As a result, a positive electrode plate having a thickness of 0.157 mm was obtained. This positive electrode plate was cut into a width of 57 mm and a length of 564 mm to obtain a positive electrode.

-Production of negative electrode-
First, silicon was vapor-deposited on each surface of a copper foil (negative electrode current collector) having a thickness of 18 μm and roughened on both surfaces by vacuum deposition. At this time, the degree of vacuum inside the vacuum vapor deposition machine was set to 1.5 × 10 ⁻³ Pa while introducing 25 sccm of oxygen into the vacuum vapor deposition machine. As a result, a silicon-containing film having a thickness of 10 μm was formed on each surface of the copper foil. From the measurement of the amount of oxygen by the combustion method and the measurement of the amount of silicon by ICP analysis, it was found that the composition of the active material contained in this silicon-containing film was SiO _0.42 .

Next, lithium was deposited on each surface of the silicon-containing film by vacuum deposition. Thereby, a lithium film having a density of 3.2 g / m ² is formed on each surface of the silicon-containing film (a lithium film having a film thickness of 6 μm when the density of lithium is converted into a film thickness of the lithium film). It was done. Thereafter, the negative electrode plate was handled in a dry air environment having a dew point of −30 ° C. or lower.

  Subsequently, an N-methyl-2-pyrrolidone solution (concentration 8 mass%) containing a polymer copolymerized at a ratio of VDF: HFP = 97: 3 (mass ratio) is applied on one surface of the negative electrode plate and dried. I let you. Thus, a polymer layer (second thin film, hereinafter referred to as “negative electrode polymer layer”) having a thickness of 1 μm was formed. Thereafter, a dimethyl carbonate solution (concentration 5 mass%) containing a polymer copolymerized at a ratio of VDF: HFP = 88: 12 (mass ratio) was applied onto the negative electrode side polymer layer and dried. As a result, a polymer layer (first thin film, hereinafter referred to as “main layer side polymer layer”) having a thickness of 1 μm was formed. Thereafter, the negative electrode plate on which the two polymer layers were formed was cut into a width of 58.5 mm and a length of 750 mm to obtain a negative electrode.

-Preparation of non-aqueous electrolyte-
A mixed solvent composed of ethylene carbonate and dimethyl carbonate mixed so that the volume ratio was 1: 3 was prepared. To this mixed solvent, 5 wt% vinylene carbonate (an additive that increases the charge / discharge efficiency of the battery) is added, and LiPF ₆ (electrolyte) is adjusted so that the molar concentration (molar concentration with respect to the mixed solvent) is 1.4 mol / m ^3. ) Was dissolved. In this way, a nonaqueous electrolytic solution was obtained.

-Fabrication of cylindrical battery-
First, a positive electrode lead made of aluminum was connected to the positive electrode current collector, and a negative electrode lead made of nickel was connected to the negative electrode current collector. Thereafter, the positive electrode and the negative electrode are arranged so that the positive electrode lead and the negative electrode lead extend in opposite directions, and a polyethylene film (main layer, thickness 20 μm) is sandwiched between the positive electrode and the main layer side polymer layer, The positive electrode, the negative electrode, and the polyethylene film were wound. Thereby, the electrode group was produced. When the total number of moles of lithium contained in the positive electrode and the negative electrode of this electrode group was determined by ICP analysis, when the total number of moles of Ni, Co and Al contained in the positive electrode was 1, the total number of moles of lithium was 1. 13.

  Next, an upper insulating film was disposed at the upper end of the electrode group, and a lower insulating plate was disposed at the lower end. Thereafter, the negative electrode lead was welded to the battery case and the positive electrode lead was welded to the sealing plate, and the electrode group was housed in the battery case. Thereafter, a non-aqueous electrolyte was injected into the battery case by a decompression method. Then, the sealing plate was caulked to the open end of the battery case via a gasket. In this way, the battery 1 was produced.

(Battery 2)
A battery 2 was produced according to the same method as the battery 1 except for the constitution of the main layer side polymer layer. Specifically, a dimethyl carbonate solution (concentration 5 mass%) containing a polymer copolymerized at a ratio of VDF: HFP = 85: 15 (mass ratio) was applied on the negative electrode side polymer layer and dried. .

(Battery 3)
A battery 3 was produced in the same manner as the battery 1 except that the thickness of the negative electrode side polymer layer was 3 μm and the thickness of the main layer side polymer layer was 5 μm.

(Battery 4)
A battery 4 was produced in the same manner as the battery 1 except that the negative electrode polymer layer was a PVDF film. Specifically, an N-methyl-2-pyrrolidone solution containing only PVDF (concentration: 12% by mass) was applied on one side of the negative electrode plate and dried.

(Battery 5)
A battery 5 was produced according to the same method as the battery 1 except that the polymer layer was not formed on the surface of the negative electrode plate.

(Battery 6)
A battery 6 was produced in the same manner as the battery 1 except that only one polymer layer was formed on one side of the negative electrode plate. Specifically, an N-methyl-2-pyrrolidone solution containing only PVDF (concentration: 12% by mass) was applied on one side of the negative electrode plate and dried. Thereafter, this negative electrode plate was cut to obtain a negative electrode.

(Battery 7)
A battery 7 was produced in the same manner as the battery 1 except that only one polymer layer was formed on one side of the negative electrode. Specifically, a dimethyl carbonate solution (concentration 5 mass%) containing a polymer copolymerized at a ratio of VDF: HFP = 88: 12 (mass ratio) was applied on one side of the negative electrode plate and dried. Thereafter, this negative electrode plate was cut to obtain a negative electrode.

2. Evaluation Method The battery voltage of a battery in which an internal short circuit has occurred is lower than the battery voltage of a battery in which no internal short circuit has occurred. The voltage of the battery of Example 1 is about 2.8V. Therefore, in Example 1, the case where the measured battery voltage was lower than 2.6 V was judged as defective, and the number of defective batteries (the number of parameters was 50) was counted.

  Specifically, the battery voltage was measured 48 hours after each of the batteries 1 to 7 was produced, and the number of batteries in which an internal short circuit occurred was counted. The result is shown in the defect rate 48 hours after assembly in FIG.

  Moreover, after carrying out 500 cycles of charging / discharging with respect to each of the batteries 1-7, the battery voltage was measured and the number of the batteries which the internal short circuit generate | occur | produced was counted. One cycle is charged at a constant current of 1.4 A under a 45 ° C. environment until the voltage reaches 4.15 V, and charged at a constant voltage of 4.15 V until the current reaches 50 mA. This is a series of operations in which discharge is performed at a constant current of 8 A until the voltage reaches 2.0V. Note that a 30-minute pause was provided between charging and discharging and between discharging and charging. This result is shown in the defect rate after 500 cycles in FIG.

[Example 2]
In Example 2, the negative electrode side polymer layer and the main layer side polymer layer were fixed on one side of a polyethylene film to produce a separator.

1. Method for producing non-aqueous electrolyte secondary battery (Battery 8)
A battery 8 was prepared according to the same method as the battery 1 except for the configuration of the negative electrode side polymer layer and the main layer side polymer layer, the negative electrode preparation method, and the negative electrode side polymer layer and main layer side polymer layer preparation method. .

-Production of negative electrode-
Specifically, lithium was vapor-deposited on each surface of the silicon-containing film by a vacuum vapor deposition method in accordance with “-Production of negative electrode” of the battery 1, and then the electrode plate was cut into a width of 58.5 mm and a length of 750 mm. did. In this way, a negative electrode was obtained.

-Production of separator-
A polyethylene film (thickness 20 μm) was immersed in N-methyl-2-pyrrolidone. Thereafter, an N-methyl-2-pyrrolidone solution (concentration 3% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 95: 5 (mass ratio) was applied on one side of the polyethylene film, and together with the polyethylene film Dried. Thereby, the main layer side polymer was formed on one side of the polyethylene film. The total of the thickness of the polyethylene film and the thickness of the main layer side polymer was 21 μm.

  Subsequently, an N-methyl-2-pyrrolidone solution containing only PVDF (concentration: 12% by mass) was applied onto the main polymer layer and then dried. The thickness after drying was 22 μm.

(Battery 9)
A battery 9 was produced according to the same method as the battery 8 except for the respective configurations of the negative electrode side polymer layer and the main layer side polymer layer.

  Specifically, a dimethyl carbonate solution (concentration of 5% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 88: 12 (mass ratio) was applied on one side of a polyethylene film and dried. The thickness after drying was 20 μm. When the cross section of the polyethylene film was observed after drying, it was found that the polymer soaked into one side of the polyethylene film.

  Next, an N-methyl-2-pyrrolidone solution (concentration 3% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 95: 5 (mass ratio) was applied onto the surface of the main polymer layer. And then dried. The average thickness after drying was 21 μm.

(Battery 10)
A battery 10 was produced according to the same method as the battery 8 except that only the main layer side polymer layer was formed on one side of the polyethylene film.

2. Evaluation Method Batteries 8 to 10 were evaluated using the same evaluation method as the evaluation method in Example 1 above. The evaluation results are shown in FIG.

Example 3
In Example 3, graphite was used as the negative electrode active material.

1. Method for producing non-aqueous electrolyte secondary battery (Battery 11)
A battery 11 was produced in the same manner as the battery 2 except that graphite was used as the negative electrode active material.

-Production of negative electrode-
First, scaly artificial graphite (negative electrode active material) was pulverized and classified so that the average particle size was about 20 μm.

  Next, 100 parts by mass of flaky artificial graphite was mixed with 3 parts by mass of styrene butadiene rubber (binder) and 100 parts by mass of an aqueous solution containing 1% by mass of carboxymethyl cellulose. This obtained the negative mix slurry.

  Subsequently, this negative electrode mixture slurry was applied onto both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm and dried, and the obtained electrode plate was rolled. As a result, a negative electrode plate having a thickness of 0.156 mm was obtained. This negative electrode plate was heat-treated with hot air at 190 ° C. for 8 hours in a nitrogen atmosphere. The negative electrode plate after the heat treatment was cut to obtain a negative electrode having a thickness of 0.156 mm, a width of 58.5 mm, and a length of 750 mm. In addition, the negative electrode active material which exists in the part (edge part in the longitudinal direction of a negative electrode) which does not oppose a positive electrode active material when forming an electrode group was removed.

  Then, an N-methyl-2-pyrrolidone solution (concentration 8% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 97: 3 (mass ratio) was applied on the surface of the negative electrode and dried. . Thereby, a negative electrode side polymer layer having a thickness of 1 μm was formed. Thereafter, a dimethyl carbonate solution (concentration of 5% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 85: 15 (mass ratio) was applied onto the surface of the negative electrode polymer layer and dried. Thereby, a main layer side polymer layer having a thickness of 1 μm was formed.

  Then, a lithium film having a thickness of 100 μm, a width of 50 mm, and a length of 50 mm was pasted on the end portion (portion where the copper foil was exposed) in the longitudinal direction of the negative electrode.

(Battery 12)
A battery 12 was produced according to the same method as the battery 11 except that the negative electrode was produced without attaching the lithium film to the copper foil.

(Battery 13)
A battery 13 was produced in the same manner as the battery 11 except that the polymer layer was not formed on the surface of the negative electrode plate.

2. Evaluation Method Using the same evaluation method as the evaluation method in Example 1, the batteries 11 to 13 were evaluated. Here, in this example, the charge end voltage was 4.2 V and the discharge end voltage was 2.5 V in the charge / discharge cycle. The evaluation results are shown in FIG.

  In this example, the capacity of the battery was measured. The battery has a capacity of 25 ° C. with a constant current of 1.4 A until the voltage reaches 4.2 V, and after charging with a constant voltage of 4.2 V until the current reaches 50 mA, the battery capacity is 0 The capacity when discharging is performed until the voltage reaches 2.5 V at a constant current of .56 A.

[Discussion]
The result of Examples 1-3 is considered based on FIGS.

Example 1
In batteries 1 to 4, the defect rate after 48 hours after assembly and the defect rate after 500 cycles were both zero. When these batteries were disassembled and the respective cross sections of the negative electrode, the negative electrode side polymer layer, and the main layer side polymer layer were observed, precipitates of metal elements such as Fe or Ni were observed in part. However, these precipitates did not reach the positive electrode beyond the separator, but were formed along the surface of the negative electrode.

  On the other hand, when a battery in which an internal short circuit occurred among the batteries 5 to 7 was analyzed in the same manner, a metal element such as Fe or Ni was deposited in a needle shape, and the deposit penetrated the separator and reached the positive electrode. .

  In each of the batteries 1 to 4 and the batteries 5 to 7, the total number of moles of metals present in the polyethylene film, the negative electrode side polymer layer, the main layer side polymer layer, and the electrolyte solution was quantified by ICP analysis. The number of moles was almost the same in batteries 1-7. That is, the amount of dissolved metal foreign matter was the same in the batteries 1 to 4 and the batteries 5 to 7. However, since the deposit shape of the metal foreign matter was different between the batteries 1 to 4 and the batteries 5 to 7, no internal short circuit occurred in the batteries 1 to 4, whereas an internal short circuit occurred in the batteries 5 to 7.

-Example 2-
The same result as in Example 1 was obtained.

Example 3
The discharge capacity of the battery 12 was smaller than the discharge capacities of the battery 11 and the battery 13. The reason is that the irreversible capacity is not compensated for the negative electrode.

  In the battery 13, since the negative electrode side polymer layer and the main layer side polymer layer are not formed, needle-like precipitates penetrate the separator and reach the positive electrode as in the batteries 5 to 7 and the battery 10, As a result, an internal short circuit occurred.

  As described above, the present invention is useful, for example, as a power source for consumer equipment, a power source mounted in an automobile, or a power source for a large tool.

1 Battery case
2 Sealing plate
3 Gasket
4 Positive electrode
4A cathode current collector
4B cathode mix layer
5 Negative electrode
5A negative electrode current collector
5B Negative electrode active material layer
6 Separator
6A Main layer
6B 1st thin film
6C second thin film
7a Upper insulation plate
7b Lower insulation plate
8 electrode group

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, there has been a demand for driving automobiles with electric energy from the viewpoint of environmental problems, and there has been a demand for direct current for power supplies for large tools and the like. In order to satisfy these requirements, there is a demand for a small and lightweight secondary battery that can be charged quickly and discharge a large current. As a typical secondary battery satisfying such a demand, a non-aqueous electrolyte secondary battery (hereinafter sometimes simply referred to as “battery”) may be mentioned.

The nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a separator. In the positive electrode, a material that reversibly electrochemically reacts with lithium ions (positive electrode active material, lithium-containing composite oxide) is held in the positive electrode current collector (see Patent Document 1). In the negative electrode, a material capable of occluding and releasing lithium (negative electrode active material such as graphite or tin alloy) is held in the negative electrode current collector (see Patent Document 2). The separator is interposed between the positive electrode and the negative electrode, prevents a short circuit from occurring between the positive electrode and the negative electrode, and holds the electrolytic solution. In the electrolytic solution, a lithium salt (for example, LiClO ₄ or LiPF ₆ ) is dissolved in an aprotic organic solvent.

  The nonaqueous electrolyte secondary battery is manufactured according to the following method. First, each of the positive electrode and the negative electrode is formed into a thin film sheet or a foil shape, and the positive electrode and the negative electrode are laminated or wound in a spiral shape via a separator. The electrode group thus produced is housed in a battery case (may be made of metal such as iron, aluminum or stainless steel, or nickel plating or the like may be applied to the case surface) A non-aqueous electrolyte is injected into the battery case. Then, the opening part of a battery case is sealed with a cover plate. An aluminum laminate film may be used instead of the metal battery case.

Japanese Patent Laid-Open No. 11-7958 Japanese Patent Laid-Open No. 11-242955

  During the production of the nonaqueous electrolyte secondary battery, a foreign substance made of metal (hereinafter referred to as “metallic foreign substance”) may be mixed. As a typical example of a metal foreign object, a metal mixed during synthesis of a positive electrode active material or a conductive agent, or a rotating part such as a bearing or a roller in a manufacturing apparatus wears during manufacturing of a nonaqueous electrolyte secondary battery. The metal piece which generate | occur | produces by can be mentioned. Therefore, examples of the metal foreign material include iron, nickel, copper, stainless steel, and brass. These metallic foreign substances are dissolved in the non-aqueous electrolyte under the operating potential of the positive electrode to form ions, and these ions are deposited as metal on the surface of the negative electrode, for example, during charging. When the metallic foreign matter deposited on the surface of the negative electrode penetrates the separator and reaches the positive electrode, an internal short circuit occurs.

  This invention is made | formed in view of this point, The objective is to provide the nonaqueous electrolyte secondary battery with which the safety | security was ensured.

  In the nonaqueous electrolyte secondary battery according to the present invention, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte are accommodated in a battery case. The separator has a main layer and a plurality of thin films. Each of the plurality of thin films has a film thickness thinner than that of the main layer, and has an ion transmittance smaller than that of the main layer. The plurality of thin films have different ion transmittances. In such a non-aqueous electrolyte secondary battery, foreign metal ions can be prevented from passing through each thin film in the thickness direction. Therefore, it can prevent that a metal foreign material ion reaches | attains on the surface of a negative electrode.

  In the nonaqueous electrolyte secondary battery according to the present invention, it is preferable that a thin film having the smallest ion permeability among a plurality of thin films is provided on the surface of the negative electrode, and a thin film having the smallest ion permeability among the plurality of thin films. Is more preferably adhered to the surface of the negative electrode. Thereby, it can suppress that a metal foreign material ion reaches | attains on the surface of a negative electrode.

  In the non-aqueous electrolyte secondary battery according to the present invention, it is preferable that the plurality of thin films are arranged so that the ion transmittance decreases from the positive electrode toward the negative electrode. Thereby, the quantity of the foreign metal ion permeate | transmitted in the thickness direction of an electrode group can be gradually reduced as it goes to a negative electrode from a positive electrode. In such a non-aqueous electrolyte secondary battery, a thin film having the largest ion permeability among a plurality of thin films may be integrated with the main layer.

  In a preferred embodiment described below, the plurality of thin films have different hexafluoropropylene concentrations, and a thin film having a high concentration of hexafluoropropylene has a larger ion permeability than a thin film having a low concentration of hexafluoropropylene. In this case, each thin film may contain a copolymer of hexafluoropropylene and vinylidene fluoride, and the thin film having the smallest ion permeability among the plurality of thin films may be made of polyvinylidene fluoride.

  In the nonaqueous electrolyte secondary battery according to the present invention, the positive electrode only needs to have a composite oxide containing lithium, a first metal (metal other than lithium), and oxygen. X / y is preferably larger than 1.05 when the total number of moles is x [mol] and the total number of moles of the first metal in the composite oxide is y [mol]. Thereby, even when the irreversible capacity is large (capacity at the first discharge is lower than the capacity at the first charge), it is possible to suppress the occurrence of an internal short circuit due to the mixing of metal foreign objects. This effect is increased when the negative electrode has silicon, tin, or a compound containing silicon or tin.

  In the present specification, “a plurality of thin films” includes a case where the boundary between thin films cannot be confirmed. For example, when thin films having a very small thickness are stacked, it may be difficult to confirm the boundary between the thin films.

  In the present specification, the “ion permeability” can be measured, for example, according to the following method. First, an electrolyte solution (A) containing a metal salt is placed on one side with a predetermined membrane (a membrane for measuring ion permeability), and a solution (B) containing no metal salt is placed on the other side. After a predetermined time has elapsed, the salt concentration in the solution (B) is measured. Alternatively, after a predetermined time has elapsed, the ionic conductivity of the solution (B) is measured, and a previously prepared calibration curve showing the relationship between the salt concentration and the ionic conductivity is used in the solution (B). Estimate the salt concentration.

  In this specification, “ion” of “ion permeability” is a cation in the non-aqueous electrolyte, and includes not only foreign metal ions but also lithium ions.

  In the present specification, “the thin film is integral with the main layer” means that the boundary between the thin film and the main layer cannot be clearly confirmed. For example, a part of the material constituting the thin film penetrates into the main layer. That is. When the main layer and the thin film are both made of resin, the thin film may be integrated with the main layer.

  In the present specification, the “surface of the positive electrode” is a surface of both surfaces of the positive electrode facing the positive electrode and the negative electrode that transfers lithium ions, and the “surface of the negative electrode” is the negative electrode and lithium ions of both surfaces of the negative electrode. This is the surface facing the positive electrode that receives and delivers.

  The present invention can provide a non-aqueous electrolyte secondary battery in which safety is guaranteed.

FIGS. 1A to 1C are cross-sectional views illustrating a state in which a metal foreign matter is deposited on the surface of the negative electrode. FIG. 2 is a longitudinal sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of an electrode group in one embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating how the foreign metal ions move in the separator in one embodiment of the present invention. FIG. 5 is a table summarizing the results of Example 1. FIG. 6 is a table summarizing the results of Example 2. FIG. 7 is a table summarizing the results of Example 3.

  When the present inventors examined the precipitation of metal foreign matter on the surface of the negative electrode, the following was found. FIGS. 1A to 1C are cross-sectional views illustrating a state in which a metal foreign matter is deposited on the surface of the negative electrode. 1A to 1C, for convenience of explanation, the film thickness of the separator 96 is shown larger than the film thicknesses of the positive electrode 94 and the negative electrode 95, and FIGS. The relationship between the film thicknesses of the positive electrode 94, the negative electrode 95, and the separator 96 shown is different from the relationship between the film thicknesses of the positive electrode, the negative electrode, and the separator in an actual nonaqueous electrolyte secondary battery.

The metal foreign matter (X) in the positive electrode 94 (especially the positive electrode active material), the metal foreign matter generated during the production of the nonaqueous electrolyte secondary battery, or the metal foreign matter generated due to wear is under the immersion potential of the positive electrode (the immersion potential is Or an ion (X ^{n +} ) that dissolves under the operating potential of the positive electrode and moves, for example, in the separator 96 toward the surface of the negative electrode 95 during charging. At this time, when the negative electrode 95 is equal to or lower than the deposition potential of the metal foreign matter, the metal foreign matter ions are deposited on the surface of the negative electrode 95 located at the shortest distance as shown in FIG.

  After the metal foreign matter 99 is deposited on the surface of the negative electrode 95, new metal foreign matter ions are preferentially deposited on the surface of the metal foreign matter 99 as shown in FIG. Therefore, the tip of the metal foreign matter 99 approaches the positive electrode 94 and finally comes into contact with the surface of the positive electrode 94 as shown in FIG. As a result, an internal short circuit occurs.

  The present inventors have completed the present invention based on the above consideration. Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiment. Moreover, below, the same code | symbol may be attached | subjected about the same member.

  In the embodiment of the present invention, a lithium ion secondary battery is taken as a specific example as a nonaqueous electrolyte secondary battery, and the configuration thereof will be described. FIG. 2 is a longitudinal sectional view of the nonaqueous electrolyte secondary battery according to the present embodiment. FIG. 3 is a cross-sectional view of the electrode group in the present embodiment.

  As shown in FIG. 2, the nonaqueous electrolyte secondary battery according to this embodiment includes a battery case 1 made of, for example, stainless steel, and an electrode group 8 accommodated in the battery case 1. In addition, a nonaqueous electrolyte is injected into the battery case 1.

  An opening 1 a is formed on the upper surface of the battery case 1. A sealing plate 2 is caulked to the opening 1a via a gasket 3, whereby the opening 1a is sealed.

  The electrode group 8 includes a positive electrode 4, a negative electrode 5, and a separator 6, and the positive electrode 4 and the negative electrode 5 are wound around the separator 6 in a spiral shape as shown in FIG. 3. An upper insulating plate 7 a is disposed above the electrode group 8, and a lower insulating plate 7 b is disposed below the electrode group 8.

  One end of an aluminum positive electrode lead 4L is attached to the positive electrode 4, and the other end of the positive electrode lead 4L is connected to a sealing plate 2 (also serving as a positive electrode terminal). One end of a negative electrode lead 5L made of nickel is attached to the negative electrode 5, and the other end of the negative electrode lead 5L is connected to the battery case 1 (also serving as a negative electrode terminal).

As shown in FIG. 3, the positive electrode 4 has a positive electrode current collector 4A and a positive electrode mixture layer 4B. The positive electrode current collector 4A is a conductive plate-like member, and is made of, for example, aluminum. The positive electrode mixture layer 4B is provided on both surfaces of the positive electrode current collector 4A, and is bonded to a positive electrode active material (a composite oxide containing lithium and a metal other than lithium (first metal) and oxygen, for example, LiCoO ₂ ). It contains an adhesive and a conductive agent.

  As shown in FIG. 3, the negative electrode 5 includes a negative electrode current collector 5A and a negative electrode active material layer 5B. The negative electrode current collector 5A is a conductive plate-like member, and is made of, for example, copper. The negative electrode active material layer 5B is provided on both surfaces of the negative electrode current collector 5A, and may contain a graphite material and a binder. Silicon, tin, a compound containing silicon, or a compound containing tin (hereinafter referred to as “tin”) Then, it is described as “metal or a compound containing a metal”).

  The separator 6 holds a non-aqueous electrolyte, and is provided between the positive electrode 4 and the negative electrode 5 as shown in FIG. The separator 6 has a main layer 6A, a first thin film 6B, and a second thin film 6C. The main layer 6 </ b> A is provided on the surface of the positive electrode 4. The main layer 6A has a high ion permeability and a predetermined mechanical strength and insulation, and is, for example, a microporous film, a woven fabric or a non-woven fabric made of polyolefin such as polypropylene or polyethylene. The second thin film 6 </ b> C is provided on the surface of the negative electrode 5 and is preferably bonded to the surface of the negative electrode 5. The first thin film 6B is sandwiched between the main layer 6A and the second thin film 6C, is preferably integral with the main layer 6A, and is preferably bonded to the second thin film 6C.

  The electrode group 8 having such a separator 6 is produced according to any of the following methods. In the first method, the second thin film 6C and the first thin film 6B are sequentially formed on the surface of the negative electrode 5, and then the main layer 6A and the first thin film 6B formed on the surface of the positive electrode 4 are formed. Wind them after bringing them into contact with each other. In the second method, the main layer 6A, the first thin film 6B, and the second thin film 6C are sequentially formed on the surface of the positive electrode 4, and then the second thin film 6C is brought into contact with the surface of the negative electrode 5. Turn around. In the third method, the first thin film 6B and the second thin film 6C are sequentially formed on the surface of the carrier (the surface of the carrier is subjected to a release treatment) and then the main body on the surface of the positive electrode 4 The first thin film 6B is peeled off from the carrier, and the first thin film 6B and the second thin film 6C are sandwiched between the main layer 6A and the negative electrode 5, and then the film is placed between the layer 6A and the negative electrode 5. Turn.

  The separator 6 in this embodiment is further shown. The main layer 6A has a larger film thickness than each of the first thin film 6B and the second thin film 6C. The thickness of the main layer 6A is, for example, 10 μm or more and 300 μm or less, preferably 10 μm or more and 40 μm or less, more preferably 15 μm or more and 30 μm or less, and most preferably 15 μm or more and 25 μm or less. The total thickness of the first thin film 6B and the second thin film 6C is, for example, 0.01 μm or more and 20 μm or less, preferably 0.1 μm or more and 15 μm or less, and preferably 0.5 μm or more and 10 μm or less. More preferably.

  If the thickness of the main layer 6A is less than 10 μm, a sufficient amount of nonaqueous electrolyte may not be retained. In addition, contact between the positive electrode 4 and the negative electrode 5 may not be avoided, and thus an internal short circuit may occur. On the other hand, if the thickness of the main layer 6 </ b> A exceeds 300 μm, the occupation ratio of the separator 6 in the electrode group 8 becomes high, so that a sufficient amount of active material may not be filled in the battery case 1.

  If the sum of the film thickness of the first thin film 6B and the film thickness of the second thin film 6C is less than 0.01 μm, it may not be possible to prevent the occurrence of an internal short circuit due to the mixing of metal foreign matter. On the other hand, when the total thickness of the first thin film 6B and the second thin film 6C exceeds 20 μm, the occupation ratio of the first thin film 6B and the second thin film 6C in the separator 6 increases. In some cases, the function of the separator 6 may be reduced. In addition, the diffusion of lithium ions in the separator 6 may be suppressed, which may cause a decrease in battery performance.

  In other words, the sum of the thickness of the first thin film 6B and the thickness of the second thin film 6C may be 0.1% or more of the thickness of the main layer 6A, and is 0.1% or more and 20%. Or less, more preferably 0.1% or more and 10% or less. If the sum of the film thickness of the first thin film 6B and the film thickness of the second thin film 6C is less than 0.1% of the thickness of the main layer 6A, it is impossible to prevent the occurrence of an internal short circuit due to the mixing of metal foreign matter. There is a case. On the other hand, if the total thickness of the first thin film 6B and the second thin film 6C exceeds 20% of the thickness of the main layer 6A, the function of the separator 6 may be deteriorated. In addition, the diffusion of lithium ions in the separator 6 may be suppressed, which may cause a decrease in battery performance.

  Furthermore, in the separator 6 in this embodiment, the main layer 6A, the first thin film 6B, and the second thin film 6C have different ion transmittances. The main layer 6A has the maximum ion transmittance, and the ion transmittance decreases in the order of the first thin film 6B and the second thin film 6C. Thereby, it is possible to prevent the occurrence of an internal short circuit due to the mixing of metal foreign matter. Below, the separator 6 in this embodiment is further demonstrated, referring FIG. FIG. 4 is a cross-sectional view illustrating how the foreign metal ions move in the separator 6 in the present embodiment. In FIG. 4, for convenience of explanation, the thickness of the separator 6 is shown larger than the thickness of each of the positive electrode 4 and the negative electrode 5, and the relationship between the thickness of the positive electrode 4, the negative electrode 5 and the separator 6 shown in FIG. Is different from the relationship of the film thicknesses of the positive electrode 4, the negative electrode 5, and the separator 6 in an actual nonaqueous electrolyte secondary battery.

  When attention is paid to the metal foreign matter mixed in the positive electrode mixture layer 4B, the metal foreign matter is dissolved as a metal ion in the nonaqueous electrolyte under the immersion potential of the positive electrode 4 or the operating potential of the positive electrode 4, for example, charging It moves toward the negative electrode 5 inside. In the separator 6, the main layer 6 </ b> A, the first thin film 6 </ b> B, and the second thin film 6 </ b> C are arranged in order from the positive electrode 4 to the negative electrode 5. For this reason, the foreign metal ions pass through the main layer 6A and arrive at the first thin film 6B. Since the first thin film 6B has an ion transmittance lower than that of the main layer 6A, some of the foreign metal ions arriving at the first thin film 6B cannot pass through the first thin film 6B, and the first thin film 6B does not pass through the first thin film 6B. It diffuses into the thin film 6B (the foreign metal ions on the left side of FIG. 4).

  The foreign metal ions transmitted through the first thin film 6B arrive at the second thin film 6C. Since the second thin film 6C has an ion transmission rate lower than that of the first thin film 6B, it is difficult for the foreign metal ions reaching the second thin film 6C to pass through the second thin film 6C. In the thin film 6C (metal foreign ion on the right side in FIG. 4). Thereby, it is possible to delay the arrival of the metal foreign matter ions to the surface of the negative electrode 5.

  Metallic foreign matter generated during the manufacture of the nonaqueous electrolyte secondary battery or metallic foreign matter caused by wear is not necessarily mixed into the positive electrode 4 and may be mixed into the main layer 6A, for example. Regardless of the position where the metal foreign matter is mixed, the metal foreign matter ions diffuse into the first thin film 6B or the second thin film 6C. Therefore, in the present embodiment, it is possible to prevent the occurrence of an internal short circuit regardless of the cause of occurrence of the metallic foreign matter.

  Even if the metal foreign matter ions that have passed through the second thin film 6C reach the surface of the negative electrode 5, the amount of the metal foreign matter ions can be kept low. Therefore, the amount of metallic foreign matter deposited on the surface of the negative electrode 5 can be reduced. In addition, the foreign metal ions transmitted through the second thin film 6C reach the surface of the negative electrode 5 after being slightly diffused in the first thin film 6B and the second thin film 6C. Therefore, it is possible to prevent the metal foreign matter from being deposited in a direction perpendicular to the surface of the negative electrode 5. From these things, in this embodiment, even if it is a case where a metal foreign material precipitates on the surface of the negative electrode 5, generation | occurrence | production of an internal short circuit can be prevented. Since the lithium ions that control the operation of the battery are much more present in the nonaqueous electrolyte than the foreign metal ions, the influence of the diffusion suppression by the first thin film 6B and the second thin film 6C and the negative electrode 5 Less susceptible to delays in reaching The present inventors have confirmed that the nonaqueous electrolyte secondary battery according to this embodiment has no problem in the operation of the battery. Each structure of the 1st thin film 6B and the 2nd thin film 6C is further demonstrated.

  The first thin film 6B and the second thin film 6C have different ion transmittances. The first thin film 6B is preferably bonded to the surfaces of the main layer 6A and the second thin film 6C, and the second thin film 6C is preferably bonded to the surface of the negative electrode 5. From these things, the 1st thin film 6B should just contain the material which can adjust ion transmittance, and the material which has adhesiveness. The second thin film 6C may include a material capable of adjusting the ion permeability and a material having an adhesive ability, or may be made of a material having an adhesive ability.

  Examples of the material capable of adjusting the ion permeability include hexafluoropropylene (hereinafter referred to as “HFP”). HFP is superior in flexibility compared to poly (vinylidene fluoride) (hereinafter referred to as “PVDF”) and so on, so that it takes in an electrolyte and swells. Therefore, HFP is excellent in affinity with the non-aqueous electrolyte. Therefore, if the concentration of HFP in the membrane is increased, the ion permeability of the membrane can be increased. Therefore, it is sufficient that the HFP concentration in the first thin film 6B is higher than the HFP concentration in the second thin film 6C. For example, the HFP concentration in the first thin film 6B is 2% by mass or more and 30% by mass or less, and the HFP concentration in the second thin film 6C is 0% by mass or more and 20% by mass or less. If the HFP concentration in the first thin film 6B is less than 2% by mass, and if the HFP concentration in the second thin film 6C exceeds 20% by mass, the first thin film 6B and the second thin film 6C Difficult to make difference in ion permeability. On the other hand, if the HFP concentration in the first thin film 6B exceeds 30% by mass, the first thin film 6B is likely to swell the nonaqueous electrolyte. Therefore, the main layer 6A, the second thin film 6C, and the first thin film It causes a decrease in adhesive strength with 6B.

  For example, PVDF, polytetrafluoroethylene, aramid resin, polyamide, and polyimide are known as materials having adhesion ability, but it is preferable that the first thin film 6B and the second thin film 6C contain PVDF. . There are three reasons for this.

  PVDF is excellent in adhesive strength. Therefore, it is possible to prevent the first thin film 6B from being peeled off from the surface of the main layer 6A or the surface of the second thin film 6C during the production of the electrode group 8, and the second thin film 6C is the surface of the first thin film 6B. Alternatively, peeling from the surface of the negative electrode 5 can be prevented.

  PVDF is excellent in flexibility. Therefore, each of the first thin film 6B and the second thin film 6C is deformed following the expansion or contraction of the negative electrode active material. Therefore, the nonaqueous electrolyte secondary battery can be charged / discharged without lowering the performance and safety, and the cycle characteristics can be prevented from lowering. This effect is increased when a metal or a compound containing a metal is used for the negative electrode active material. This is because, when the negative electrode active material is a metal or a compound containing a metal, the amount of expansion and contraction of the negative electrode active material due to charge / discharge is larger than when the negative electrode active material is a carbon material. This is because the amount of deformation of the first thin film 6B and the second thin film 6C due to the expansion and contraction of the active material increases.

  PVDF is electrically stable in the voltage range in which the nonaqueous electrolyte secondary battery operates, and does not react with the nonaqueous electrolyte.

  In view of the above, the first thin film 6B preferably contains 2% by mass or more and 30% by mass or less of HFP and PVDF, for example, 2% by mass or more and 30% by mass or less of HFP and VDF. It only has to be united. If the 1st thin film 6B consists of this copolymer, the softness | flexibility of VDF can be improved. Accordingly, the first thin film 6B is preferably made of a copolymer of HFP and VDF in an amount of 2% by mass to 30% by mass.

  The second thin film 6C preferably contains 0 mass% or more and 20 mass% or less of HFP and PVDF, for example, a copolymer of HFP and VDF of 20 mass% or less (excluding 0 mass%). It may consist of PVDF or PVDF. If the 2nd thin film 6C consists of this copolymer, the softness | flexibility of VDF can be improved. Therefore, the second thin film 6C is preferably made of a copolymer of HFP and VDF of 20% by mass or less (excluding 0% by mass).

  The second thin film 6C will be further described. Since the second thin film 6C has less HFP than the first thin film 6B, the second thin film 6C has more adhesive material than the first thin film 6B. Therefore, since the second thin film 6C has better adhesiveness than the first thin film 6B, the first thin film 6B can be bonded to the surface of the negative electrode 5 via the second thin film 6C. As described above, the second thin film 6C has a function of adhering the first thin film 6B to the negative electrode 5 in addition to the function of making it difficult to diffuse foreign metal ions as compared with the first thin film 6B.

  As described above, in the present embodiment, the separator 6 includes the first thin film 6B and the second thin film 6C. Accordingly, the foreign metal ions are diffused into the first thin film 6B or the second thin film 6C, so that the foreign metal ions can be prevented from reaching the surface of the negative electrode 5. Even if the metal foreign matter ions reach the surface of the negative electrode 5, the metal foreign matter is deposited in a direction substantially parallel to the surface of the negative electrode 5. Therefore, it is possible to prevent the metal foreign matter from being concentrated and deposited on one place of the negative electrode 5, thereby preventing the occurrence of an internal short circuit due to the contamination of the metal foreign matter, and thus the non-aqueous electrolyte 2 having excellent safety. Next battery can be provided.

  Furthermore, in the present embodiment, the main layer 6A, the first thin film 6B, and the second thin film 6C are arranged in this order from the positive electrode 4 toward the negative electrode 5. Therefore, the foreign metal ions that have passed through the film having the highest ion permeability (main layer 6A) can be diffused into the film having the medium ion permeability (first thin film 6B). In addition, foreign metal ions that have passed through a film having a moderate ion permeability (first thin film 6B) can be diffused into the film having the lowest ion permeability (second thin film 6C). Therefore, foreign metal ions can be efficiently diffused into the first thin film 6B or the second thin film 6C.

  In the present embodiment, the first thin film 6B is bonded to the surface of the negative electrode 5 via the second thin film 6C, and is integral with the main layer 6A. Therefore, the effect that the ion transmittance decreases stepwise from the positive electrode 4 toward the negative electrode 5 can be sufficiently exhibited. Further, it is possible to prevent a decrease in manufacturing yield of the electrode group 8.

  In the present embodiment, each of the first thin film 6B and the second thin film 6C is deformed following the expansion or contraction of the negative electrode active material. Therefore, it can prevent that performance and safety fall during charge / discharge, and can prevent the fall of cycling characteristics.

  In the present embodiment, the total thickness of the first thin film 6B and the second thin film 6C is much smaller than the thickness of the main layer 6A. Therefore, in this embodiment, since lithium ion diffusion is ensured, battery performance can be ensured.

  When the separator 6 in this embodiment is used when lithium is added to the negative electrode before forming the electrode group, a great effect can be obtained. This is specifically shown below.

  The nonaqueous electrolyte secondary battery generally has a problem that the capacity at the first discharge is low (the irreversible capacity is large) compared to the capacity at the first charge. This is because an irreversible reaction such as film formation occurs in the carbon material, which is the negative electrode active material, or a metal or a compound containing a metal during the initial charge. In order to solve this problem, a technique of adding lithium to the negative electrode before forming an electrode group has been proposed (for example, Japanese Patent Application Laid-Open No. 2005-085633).

  However, when a nonaqueous electrolyte secondary battery is manufactured using the above technique, a potential difference is generated between the positive electrode and the negative electrode immediately after the nonaqueous electrolyte is injected into the battery case. Therefore, immediately after injecting the nonaqueous electrolyte into the battery case, the metal foreign matter in the positive electrode is dissolved in the nonaqueous electrolyte and deposited on the surface of the negative electrode. Therefore, compared to the case where a non-aqueous electrolyte secondary battery is manufactured without using the above technique, an internal short circuit due to the mixing of metal foreign matter is likely to occur. For example, even when the amount of mixed metal foreign matter is not so large, an internal short circuit occurs.

  However, when the separator 6 in this embodiment is used, the metal foreign matter in the positive electrode 4 is dissolved in the nonaqueous electrolyte and then diffuses into the first thin film 6B or the second thin film 6C. Can be prevented from being deposited on the surface of the negative electrode 5. Therefore, in this embodiment, even when the dissolution of the metallic foreign matter starts immediately after the nonaqueous electrolyte is injected into the battery case, it is possible to prevent the occurrence of an internal short circuit due to the contamination of the metallic foreign matter.

In order to solve the problem of large irreversible capacity, the nonaqueous electrolyte secondary battery only needs to satisfy x / y> 1.05. Here, x is the total number of moles of lithium contained in the positive electrode and the negative electrode, and y is the first metal in the positive electrode active material (for example, when the positive electrode active material is LiCoO ₂ , the first metal is Co. X and y can be obtained, for example, by ICP (inductively coupled plasma) analysis. In the positive electrode active material, the molar ratio of lithium to the first metal is usually 1: 1 to 1.02. Therefore, if x / y> 1.05 is satisfied, lithium is added to the negative electrode before the electrode group is formed.

  The problem that irreversible capacity is large can be solved, so that x / y is large. However, if x / y is too large, the amount of lithium remaining in the negative electrode 5 (lithium that does not contribute to charging / discharging) increases, and the thermal stability of the negative electrode 5 may decrease. Further, when lithium enters the negative electrode active material, the negative electrode active material expands, causing the negative electrode 5 to expand. In the state where the negative electrode 5 is expanded, the non-aqueous electrolyte input / output ability is reduced, and thus the cycle characteristics may be deteriorated. From these facts, 1.05 <x / y ≦ 1.50 is preferable, and 1.05 <x / y ≦ 1.25 is more preferable.

  As a method of adding lithium to the negative electrode before forming the electrode group, lithium may be deposited on the surface of the negative electrode active material layer 5B, or lithium may be part of the negative electrode current collector 5A or the negative electrode active material layer 5B. (For example, a lithium film is adhered to the surface of the negative electrode active material layer 5B, or the lithium film is welded to a portion of the negative electrode current collector where the negative electrode active material layer is not formed).

  Nowadays, there is a demand for higher capacity of nonaqueous electrolyte secondary batteries. In order to meet this demand, it has been proposed to use not a carbon material but a metal or a compound containing a metal as a negative electrode active material. However, when the negative electrode active material is a metal or a compound containing a metal, the irreversible capacity increases as compared with the case where the negative electrode active material is a carbon material. Therefore, the effect of preventing the occurrence of an internal short circuit due to the mixing of foreign metal is that lithium is added to the negative electrode before forming the electrode group, and the negative electrode active material is a metal or a compound containing a metal. If you become very large.

  In addition, in this embodiment, you may have the structure shown below.

  The arrangement of the main layer 6A, the first thin film 6B, and the second thin film 6C in the separator 6 is not limited to the arrangement shown in FIG. 3, and may be the arrangement shown below. In the first arrangement, the first thin film 6B is provided on the surface of the positive electrode 4, the second thin film 6C is provided on the surface of the negative electrode 5, and the main layer 6A is formed with the first thin film 6B. It is sandwiched between the second thin film 6C. However, with this arrangement, the ion permeability cannot be reduced step by step from the positive electrode 4 toward the negative electrode 5. Therefore, there may be a case where the metal foreign matter ions cannot be efficiently diffused into the first thin film 6B or the second thin film 6C.

  In the second arrangement, the first thin film 6B and the second thin film 6C are arranged opposite to each other in the arrangement shown in FIG. 3, and in the third arrangement, the first thin film 6B and the first thin film 6B are arranged in the first arrangement. The second thin film 6C is disposed opposite to each other. However, in the second and third arrangements, the first thin film 6B is provided directly on the surface of the negative electrode 5 without passing through the second thin film 6C. Therefore, the adhesive strength between the first thin film 6B and the negative electrode 5 may not be ensured.

  In the fourth arrangement, the main layer 6A is provided on the surface of the negative electrode 5, the first thin film 6B is provided on the surface of the positive electrode 4, and the second thin film 6C is connected to the main layer 6A and the first layer. Between the two thin films 6B. In the fifth arrangement, the first thin film 6B and the second thin film 6C are arranged opposite to each other in the fourth arrangement. However, in the fourth and fifth arrangements, the main layer 6A is provided on the surface of the negative electrode 5 instead of the first thin film 6B and the second thin film 6C. For this reason, metal foreign matter ions may be deposited on the surface of the negative electrode 5, and the metal foreign matter deposited on the surface of the negative electrode 5 may reach the positive electrode 4 as shown in FIG.

  From the above, the arrangement shown in FIG. 3 is preferable to the first to fifth arrangements. However, in the 1st-5th arrangement | positioning, generation | occurrence | production of the internal short circuit resulting from mixing of a metal foreign material can be prevented compared with the case where a separator does not have a 1st thin film and a 2nd thin film. Therefore, the effects in the present embodiment can be obtained to some extent even in the first to fifth arrangements.

  The separator 6 preferably has a first thin film 6B and a second thin film 6C. If the separator does not have the second thin film 6C, the metal foreign matter ions may reach the surface of the negative electrode 5, and therefore it may not be possible to prevent the occurrence of an internal short circuit due to the contamination of the metal foreign matter. Moreover, since it is difficult to adhere the first thin film 6B to the negative electrode 5 or the like, the production yield of the electrode group 8 may be reduced, and the first thin film 6B is caused by expansion and contraction of the negative electrode active material. It may peel from the negative electrode 5 or the like. Further, if the separator 6 does not have the first thin film 6B, the metal foreign matter ions may not be sufficiently diffused. For this reason, the metal foreign matter is deposited intensively at one place and short-circuited. It may cause a malfunction that leads to

  The separator 6 may have three or more thin films. In this case, it is preferable that the three or more thin films are arranged so that the ion transmittance decreases from the positive electrode 4 toward the negative electrode 5 for the reason described above. However, if the number of thin films increases too much, the occupancy rate of the thin films in the separator 6 increases, causing a decrease in the function of the separator 6. Further, if the number of thin films is increased without changing the total thickness of the thin films, the thickness of each thin film becomes very thin, so that it is difficult to form each thin film. What is necessary is just to determine the number of thin films in consideration of these. If the number of thin films is increased without changing the total thickness of the thin films, the boundary between the thin films may not be confirmed.

  When the separator 6 has two thin films, the film thickness of the first thin film 6B may be substantially the same as the film thickness of the second thin film 6C (for example, the film thickness of the first thin film 6B). May be 40% or more and 60% or less of the total thickness of the first thin film 6B and the second thin film 6C), or may be much thinner than the thickness of the second thin film 6C. It may be much thicker than the film thickness of the second thin film 6C. In any case, the effect of the present embodiment can be obtained. However, if the film thickness of the first thin film 6B is substantially the same as the film thickness of the second thin film 6C, both the effect produced by the first thin film 6B and the effect produced by the second thin film 6C can be obtained in a balanced manner. be able to. Therefore, the film thickness of the first thin film 6B is preferably substantially the same as the film thickness of the second thin film 6C.

  The electrode group 8 may be formed by laminating the positive electrode 4 and the negative electrode 5 with the separator 6 interposed therebetween.

  The nonaqueous electrolyte secondary battery may include a positive electrode current collector plate instead of the positive electrode lead 4L, and may include a negative electrode current collector plate instead of the negative electrode lead 5L. If current collection is performed using the current collector plate, the resistance during current collection can be reduced as compared with the case where current collection is performed using leads, so that the output of the nonaqueous electrolyte secondary battery can be increased.

  The nonaqueous electrolyte secondary battery may include a laminate film instead of the battery case 1. If the electrode group 8 is wrapped with a laminate film, the amount of metal foreign matter derived from the metal case can be reduced as compared with the case where the electrode group 8 is accommodated in the battery case 1 made of metal. This can contribute to the effect of preventing the occurrence of an internal short circuit due to the mixing of foreign matter.

  Below, each structure, material, and manufacturing method of the positive electrode 4 and the negative electrode 5, the structure of 6 A of main layers of the separator 6, the material of a nonaqueous electrolyte, and the manufacturing method of a nonaqueous electrolyte secondary battery are shown.

-Positive electrode-
The positive electrode current collector 4A may be made of aluminum or a conductive material mainly composed of aluminum. The positive electrode current collector 4A may be a long conductive substrate or a long foil, and may have a plurality of holes.

  The thickness of the positive electrode current collector 4A is preferably 1 μm or more and 500 μm or less, and more preferably 10 μm or more and 20 μm or less. Thereby, the positive electrode 4 can be reduced in weight while maintaining the strength of the positive electrode 4.

The positive electrode active material is a composite oxide containing lithium, a first metal, and oxygen. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiCoNiO ₂ , LiCo _1-z M _z O ₂ , LiNi _1-z M _{z O 2, LiNi 1/3 Co 1/3} Mn 1/3 O 2, LiMn 2 O 4, LiMnMO 4, a LiMePO ₄ or _Li 2 MePO ₄ F. M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Me is at least one selected from Fe, Mn, Co and Ni. z is greater than 0 and less than or equal to 1. Thus, the composite oxide includes a phosphate compound. The positive electrode active material may be one in which a part of the elements of the composite oxide is replaced with another element. The positive electrode active material may be a metal oxide, lithium oxide, or a composite oxide surface-treated with a conductive agent, and the surface treatment is, for example, a hydrophobic treatment.

  The average particle size of the positive electrode active material is preferably 5 μm or more and 20 μm or less. When the average particle diameter of the positive electrode active material is less than 5 μm, the surface area of the active material particles becomes extremely large, and therefore the amount of the binder necessary for fixing the active material in the electrode plate increases. For this reason, the amount of the positive electrode active material per electrode plate is reduced, which may cause a decrease in capacity. On the other hand, when the average particle diameter of the positive electrode active material exceeds 20 μm, streaks may occur on the surface of the slurry layer when the positive electrode mixture slurry is applied to the positive electrode current collector 4A. Therefore, the average particle size of the positive electrode active material is preferably 5 μm or more and 20 μm or less.

  Examples of the binder include PVDF, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, polyacrylic acid ethyl ester, and polyacrylic acid. Hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene butadiene rubber or carboxymethylcellulose Etc. Alternatively, the binder may be tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid and hexadiene. It is a copolymer or a mixture comprising two or more selected materials.

  Among the materials listed above, PVDF and its derivatives are chemically stable in the non-aqueous electrolyte secondary battery, and can sufficiently bind the positive electrode current collector 4A and the positive electrode active material or conductive agent, Furthermore, the positive electrode active material and the conductive agent can be sufficiently bound. Therefore, when PVDF or a derivative thereof is used as the binder, a nonaqueous electrolyte secondary battery excellent in cycle characteristics and discharge performance can be provided. In addition, since PVDF and its derivatives are inexpensive, the production cost of the nonaqueous electrolyte secondary battery can be suppressed by using PVDF or its derivatives as the binder. From the above, it is preferable to use PVDF or a derivative thereof as a binder. When PVDF is used as the binder, a positive electrode mixture slurry may be prepared using a solution in which PVDF is dissolved in N-methylpyrrolidone, and powdered PVDF is dissolved in the positive electrode mixture slurry. May be.

  The conductive agent may be, for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black (AB) or ketjen black, carbon fiber, or metal Conductive fibers such as fibers may be used, carbon fluoride may be used, metal powders such as aluminum may be used, and conductive whiskers such as zinc oxide or potassium titanate may be used. It may be a conductive metal oxide such as titanium oxide or an organic conductive material such as a phenylene derivative.

  A method for manufacturing such a positive electrode 4 will be described. First, a positive electrode mixture slurry is prepared by mixing a positive electrode active material, a binder, and a conductive agent with liquid components. At this time, the positive electrode mixture slurry only needs to contain a binder of 3.0 vol% or more and 6.0 vol% or less with respect to the positive electrode active material. Next, the obtained positive electrode mixture slurry is applied on both surfaces of the positive electrode current collector 4A and dried, and the obtained positive electrode plate is rolled. Thereby, a positive electrode having a predetermined thickness is produced.

-Negative electrode-
The negative electrode current collector 5A is preferably made of stainless steel, nickel, copper, or the like. The negative electrode current collector 5A may be a long conductive substrate or a long foil, and may have a plurality of holes.

  The thickness of the negative electrode current collector 5A is preferably 1 μm or more and 500 μm or less, and more preferably 10 μm or more and 20 μm or less. Thereby, the negative electrode 5 can be reduced in weight while maintaining the strength of the negative electrode 5.

Examples of the negative electrode active material include carbon materials, metals, metal fibers, oxides, nitrides, silicon compounds, tin compounds, and various alloy materials. The carbon material is, for example, various natural graphites, cokes, graphitized carbon, carbon fibers, spherical carbon, various artificial graphites, or amorphous carbon. The silicon compound may be SiO _x (where 0.05 <x <1.95), and a part of Si may be B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, It may be a silicon alloy substituted with at least one element selected from the group consisting of Mn, Nb, Ta, V, W, Zn, C, N and Sn, or may be a silicon solid solution. . In addition, the tin compound may be, for example, Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _x (where 0 <x <2), SnO ₂ or SnSiO ₃ . The negative electrode active material may be used alone or in combination of two or more of the materials listed above.

  A method for producing such a negative electrode 5 will be described. When a carbon material is used as the negative electrode active material, first, a negative electrode active material (carbon material) and a binder are mixed with a liquid component to prepare a negative electrode mixture slurry. Next, the obtained negative electrode mixture slurry is applied on both surfaces of the negative electrode current collector 5A and dried, and the obtained negative electrode plate is rolled. Thereby, the negative electrode 5 having a predetermined thickness is produced.

  When a metal or a compound containing a metal is used as the negative electrode active material, the negative electrode active material may be vapor-deposited on both surfaces of the negative electrode current collector 5A.

  The negative electrode 5 may be preliminarily provided with lithium for supplementing the irreversible capacity.

-Separator-
The configuration of the separator 6 is as shown in the first embodiment. The main layer 6A may have the following configuration.

  The main layer 6A may be one (insulating porous particles) in which insulating particles (for example, metal oxide or metal sulfide) are bound to each other, or a microporous thin film, a woven fabric or a nonwoven fabric made of polyolefin. You may have both with a porous insulating film. The insulating particles preferably have excellent insulating properties and are resistant to deformation even at high temperatures, and the porous insulating film is made of an insulating fine powder made of an oxide such as aluminum oxide, magnesium oxide or titanium oxide. It is preferable that it is applied on top. If a microporous thin film, a woven fabric, or a nonwoven fabric made of polyolefin is used as the main layer 6A, the main layer 6A has a shutdown function, so that the temperature increase of the nonaqueous electrolyte secondary battery can be suppressed. On the other hand, if a porous insulating film is used as the main layer 6A, the shrinkage of the main layer 6A can be prevented even when the temperature of the nonaqueous electrolyte secondary battery becomes very high (eg, 200 ° C. or higher). The occurrence of a short circuit can be prevented. What is necessary is just to select the structure of 6 A of main body layers according to the use etc. of a nonaqueous electrolyte secondary battery.

  When a microporous thin film is used as the main layer 6A, the main layer 6A may be a single layer film made of one kind of material or a composite film made of two or more kinds of materials, It may be a multilayer film in which two or more layers made of different materials are laminated.

  The main layer 6A preferably has a porosity of 30% to 70%, and more preferably has a porosity of 35% to 60%. The porosity is the ratio of the volume of the holes to the total volume of the main layer 6A.

-Non-aqueous electrolyte-
The non-aqueous electrolyte may be a liquid non-aqueous electrolyte, a gel-like non-aqueous electrolyte, or a solid non-aqueous electrolyte.

  In a liquid nonaqueous electrolyte (nonaqueous electrolyte solution, which will be described later), an electrolyte (for example, a lithium salt) is dissolved in a nonaqueous solvent.

  In the gel-like nonaqueous electrolyte, the nonaqueous electrolyte is held by the polymer material. Examples of the polymer material include PVDF, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, polyacrylate, and polyvinylidene fluoride hexafluoropropylene.

  The solid non-aqueous electrolyte includes a polymer solid electrolyte.

  Below, it shows about a non-aqueous electrolyte.

  As the non-aqueous solvent, a known non-aqueous solvent can be used, and for example, a cyclic carbonate, a chain carbonate, or a cyclic carboxylic acid ester can be used. The cyclic carbonate is, for example, propylene carbonate (PC) or ethylene carbonate (EC). The chain carbonate is, for example, diethyl carbonate (DEC), ethyl methyl carbonate (EMC) or dimethyl carbonate (DMC). The cyclic carboxylic acid ester is, for example, γ-butyrolactone (GBL; gamma-butyrolactone) or γ-valerolactone (GVL). As the non-aqueous solvent, one of the non-aqueous solvents listed above may be used alone, or two or more thereof may be used in combination.

Examples of the electrolyte include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr , LiI, chloroborane lithium, borates, or imide salts. Examples of the borate salts include bis (1,2-benzenediolate (2-)-O, O ′) lithium borate, bis (2,3-naphthalenedioleate (2-)-O, O ′) boron. Lithium acid, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, or bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) boron Lithium acid. Examples of the imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate (LiN (CF ₃ SO ₂ ) (C ₄ F ₉ ). SO _2)), or a bispentafluoroethanesulfonyl imide lithium _{((C 2 F 5 SO 2} ) 2 NLi). As the electrolyte, one of the electrolytes listed above may be used alone, or two or more may be used in combination.

The concentration of the electrolyte is preferably 0.5 mol / m ³ or more and 2 mol / m ³ or less.

  The nonaqueous electrolytic solution may contain the following additives in addition to the nonaqueous solvent and the electrolyte. This additive is decomposed on the surface of the negative electrode active material layer, whereby a film having high lithium ion conductivity is formed on the surface of the negative electrode active material layer. Therefore, the charge / discharge efficiency of the nonaqueous electrolyte secondary battery can be increased. Examples of the additive having such a function include vinylene carbonate (VC), 4-methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4-ethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, 4 -Propylene vinylene carbonate, 4,5-dipropyl vinylene carbonate, 4-phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl ethylene carbonate (VEC), or divinyl ethylene carbonate. As an additive, one of the materials listed above may be used alone, or two or more of the materials listed above may be used in combination. As an additive, it is preferable to use at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate. The additive may be one in which some of the hydrogen atoms in the materials listed above are substituted with fluorine atoms.

  The nonaqueous electrolytic solution may contain a benzene derivative in addition to the nonaqueous solvent and the electrolyte. The benzene derivative preferably has a phenyl group, and preferably has a phenyl group and a cyclic compound group bonded to positions adjacent to each other. Here, the benzene derivative is, for example, cyclohexylbenzene, biphenyl, or diphenyl ether. The cyclic compound group is, for example, a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, or a phenoxy group. As the benzene derivative, one of the materials listed above may be used alone, or two or more of the materials listed above may be used in combination. In addition, the nonaqueous solvent should just contain 10 vol% or less of benzene derivatives. If the non-aqueous electrolyte contains such a benzene derivative, during overcharge, the benzene derivative is decomposed and a film is formed on the surface of the electrode, thereby inactivating the non-aqueous electrolyte secondary battery. Can do.

  A method for manufacturing a nonaqueous electrolyte secondary battery will be described. First, the positive electrode lead 4L is connected to a portion of the positive electrode current collector 4A where the positive electrode mixture layer 4B is not provided, and the negative electrode lead 5L is connected to a portion of the negative electrode current collector 5A where the negative electrode active material layer 5B is not provided. Connect. Next, the positive electrode 4 and the negative electrode 5 are wound through the separator 6 to produce the electrode group 8. At this time, it is confirmed that the positive electrode lead 4L and the negative electrode lead 5L extend in opposite directions. Subsequently, the upper insulating plate 7 a is disposed at the upper end of the electrode group 8, and the lower insulating plate 7 b is disposed at the lower end of the electrode group 8. Then, the negative electrode lead 5 </ b> L is connected to the battery case 1, the positive electrode lead 4 </ b> L is connected to the sealing plate 2, and the electrode group 8 is accommodated in the battery case 1. Thereafter, a non-aqueous electrolyte is injected into the battery case 1 by a decompression method. Then, the opening 1 a of the battery case 1 is sealed with the sealing plate 2 via the gasket 3.

  Examples of the present invention will be described below. In addition, this invention is not limited to the Example shown below.

[Example 1]
1. Manufacturing method of non-aqueous electrolyte secondary battery (Battery 1)
-Production of positive electrode-
First, LiNi _0.82 Co _0.15 Al _0.03 O ₂ (positive electrode active material) having an average particle diameter of 10 μm was prepared.

Next, 4.5 parts by mass of acetylene black (conductive agent) and 4.7 parts by mass of PVDF (binder) are added to 100 parts by mass of LiNi _0.82 Co _0.15 Al _0.03 O _2. A solution dissolved in a solvent of N-methylpyrrolidone (NMP, NMP is an abbreviation for N-methylpyrrolidone) was mixed. As a result, a positive electrode mixture slurry was obtained.

  This positive electrode mixture slurry was applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm and dried, and the obtained electrode plate was rolled. As a result, a positive electrode plate having a thickness of 0.157 mm was obtained. This positive electrode plate was cut into a width of 57 mm and a length of 564 mm to obtain a positive electrode.

-Production of negative electrode-
First, silicon was vapor-deposited on each surface of a copper foil (negative electrode current collector) having a thickness of 18 μm and roughened on both surfaces by vacuum deposition. At this time, the degree of vacuum inside the vacuum vapor deposition machine was set to 1.5 × 10 ⁻³ Pa while introducing 25 sccm of oxygen into the vacuum vapor deposition machine. As a result, a silicon-containing film having a thickness of 10 μm was formed on each surface of the copper foil. From the measurement of the amount of oxygen by the combustion method and the measurement of the amount of silicon by ICP analysis, it was found that the composition of the active material contained in this silicon-containing film was SiO _0.42 .

Next, lithium was deposited on each surface of the silicon-containing film by vacuum deposition. Thereby, a lithium film having a density of 3.2 g / m ² is formed on each surface of the silicon-containing film (a lithium film having a film thickness of 6 μm when the density of lithium is converted into a film thickness of the lithium film). It was done. Thereafter, the negative electrode plate was handled in a dry air environment having a dew point of −30 ° C. or lower.

  Subsequently, an N-methyl-2-pyrrolidone solution (concentration 8 mass%) containing a polymer copolymerized at a ratio of VDF: HFP = 97: 3 (mass ratio) is applied on one surface of the negative electrode plate and dried. I let you. Thus, a polymer layer (second thin film, hereinafter referred to as “negative electrode polymer layer”) having a thickness of 1 μm was formed. Thereafter, a dimethyl carbonate solution (concentration 5 mass%) containing a polymer copolymerized at a ratio of VDF: HFP = 88: 12 (mass ratio) was applied onto the negative electrode side polymer layer and dried. As a result, a polymer layer (first thin film, hereinafter referred to as “main layer side polymer layer”) having a thickness of 1 μm was formed. Thereafter, the negative electrode plate on which the two polymer layers were formed was cut into a width of 58.5 mm and a length of 750 mm to obtain a negative electrode.

-Preparation of non-aqueous electrolyte-
A mixed solvent composed of ethylene carbonate and dimethyl carbonate mixed so that the volume ratio was 1: 3 was prepared. To this mixed solvent, 5 wt% vinylene carbonate (an additive that increases the charge / discharge efficiency of the battery) is added, and LiPF ₆ (electrolyte) is adjusted so that the molar concentration (molar concentration with respect to the mixed solvent) is 1.4 mol / m ^3. ) Was dissolved. In this way, a nonaqueous electrolytic solution was obtained.

-Fabrication of cylindrical battery-
First, a positive electrode lead made of aluminum was connected to the positive electrode current collector, and a negative electrode lead made of nickel was connected to the negative electrode current collector. Thereafter, the positive electrode and the negative electrode are arranged so that the positive electrode lead and the negative electrode lead extend in opposite directions, and a polyethylene film (main layer, thickness 20 μm) is sandwiched between the positive electrode and the main layer side polymer layer, The positive electrode, the negative electrode, and the polyethylene film were wound. Thereby, the electrode group was produced. When the total number of moles of lithium contained in the positive electrode and the negative electrode of this electrode group was determined by ICP analysis, when the total number of moles of Ni, Co and Al contained in the positive electrode was 1, the total number of moles of lithium was 1. 13.

  Next, an upper insulating film was disposed at the upper end of the electrode group, and a lower insulating plate was disposed at the lower end. Thereafter, the negative electrode lead was welded to the battery case and the positive electrode lead was welded to the sealing plate, and the electrode group was housed in the battery case. Thereafter, a non-aqueous electrolyte was injected into the battery case by a decompression method. Then, the sealing plate was caulked to the open end of the battery case via a gasket. In this way, the battery 1 was produced.

(Battery 2)
A battery 2 was produced according to the same method as the battery 1 except for the constitution of the main layer side polymer layer. Specifically, a dimethyl carbonate solution (concentration 5 mass%) containing a polymer copolymerized at a ratio of VDF: HFP = 85: 15 (mass ratio) was applied on the negative electrode side polymer layer and dried. .

(Battery 3)
A battery 3 was produced in the same manner as the battery 1 except that the thickness of the negative electrode side polymer layer was 3 μm and the thickness of the main layer side polymer layer was 5 μm.

(Battery 4)
A battery 4 was produced in the same manner as the battery 1 except that the negative electrode polymer layer was a PVDF film. Specifically, an N-methyl-2-pyrrolidone solution containing only PVDF (concentration: 12% by mass) was applied on one side of the negative electrode plate and dried.

(Battery 5)
A battery 5 was produced according to the same method as the battery 1 except that the polymer layer was not formed on the surface of the negative electrode plate.

(Battery 6)
A battery 6 was produced in the same manner as the battery 1 except that only one polymer layer was formed on one side of the negative electrode plate. Specifically, an N-methyl-2-pyrrolidone solution containing only PVDF (concentration: 12% by mass) was applied on one side of the negative electrode plate and dried. Thereafter, this negative electrode plate was cut to obtain a negative electrode.

(Battery 7)
A battery 7 was produced in the same manner as the battery 1 except that only one polymer layer was formed on one side of the negative electrode. Specifically, a dimethyl carbonate solution (concentration 5 mass%) containing a polymer copolymerized at a ratio of VDF: HFP = 88: 12 (mass ratio) was applied on one side of the negative electrode plate and dried. Thereafter, this negative electrode plate was cut to obtain a negative electrode.

2. Evaluation Method The battery voltage of a battery in which an internal short circuit has occurred is lower than the battery voltage of a battery in which no internal short circuit has occurred. The voltage of the battery of Example 1 is about 2.8V. Therefore, in Example 1, the case where the measured battery voltage was lower than 2.6 V was judged as defective, and the number of defective batteries (the number of parameters was 50) was counted.

  Specifically, the battery voltage was measured 48 hours after each of the batteries 1 to 7 was produced, and the number of batteries in which an internal short circuit occurred was counted. The result is shown in the defect rate 48 hours after assembly in FIG.

  Moreover, after carrying out 500 cycles of charging / discharging with respect to each of the batteries 1-7, the battery voltage was measured and the number of the batteries which the internal short circuit generate | occur | produced was counted. One cycle is charged at a constant current of 1.4 A under a 45 ° C. environment until the voltage reaches 4.15 V, and charged at a constant voltage of 4.15 V until the current reaches 50 mA. This is a series of operations in which discharge is performed at a constant current of 8 A until the voltage reaches 2.0V. Note that a 30-minute pause was provided between charging and discharging and between discharging and charging. This result is shown in the defect rate after 500 cycles in FIG.

[Example 2]
In Example 2, the negative electrode side polymer layer and the main layer side polymer layer were fixed on one side of a polyethylene film to produce a separator.

1. Method for producing non-aqueous electrolyte secondary battery (Battery 8)
A battery 8 was prepared according to the same method as the battery 1 except for the configuration of the negative electrode side polymer layer and the main layer side polymer layer, the negative electrode preparation method, and the negative electrode side polymer layer and main layer side polymer layer preparation method. .

-Production of negative electrode-
Specifically, lithium was vapor-deposited on each surface of the silicon-containing film by a vacuum vapor deposition method in accordance with “-Production of negative electrode” of the battery 1, and then the electrode plate was cut into a width of 58.5 mm and a length of 750 mm. did. In this way, a negative electrode was obtained.

-Production of separator-
A polyethylene film (thickness 20 μm) was immersed in N-methyl-2-pyrrolidone. Thereafter, an N-methyl-2-pyrrolidone solution (concentration 3% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 95: 5 (mass ratio) was applied on one side of the polyethylene film, and together with the polyethylene film Dried. Thereby, the main layer side polymer was formed on one side of the polyethylene film. The total of the thickness of the polyethylene film and the thickness of the main layer side polymer was 21 μm.

  Subsequently, an N-methyl-2-pyrrolidone solution containing only PVDF (concentration: 12% by mass) was applied onto the main polymer layer and then dried. The thickness after drying was 22 μm.

(Battery 9)
A battery 9 was produced according to the same method as the battery 8 except for the respective configurations of the negative electrode side polymer layer and the main layer side polymer layer.

  Specifically, a dimethyl carbonate solution (concentration of 5% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 88: 12 (mass ratio) was applied on one side of a polyethylene film and dried. The thickness after drying was 20 μm. When the cross section of the polyethylene film was observed after drying, it was found that the polymer soaked into one side of the polyethylene film.

  Next, an N-methyl-2-pyrrolidone solution (concentration 3% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 95: 5 (mass ratio) was applied onto the surface of the main polymer layer. And then dried. The average thickness after drying was 21 μm.

(Battery 10)
A battery 10 was produced according to the same method as the battery 8 except that only the main layer side polymer layer was formed on one side of the polyethylene film.

2. Evaluation Method Batteries 8 to 10 were evaluated using the same evaluation method as the evaluation method in Example 1 above. The evaluation results are shown in FIG.

Example 3
In Example 3, graphite was used as the negative electrode active material.

1. Method for producing non-aqueous electrolyte secondary battery (Battery 11)
A battery 11 was produced in the same manner as the battery 2 except that graphite was used as the negative electrode active material.

-Production of negative electrode-
First, scaly artificial graphite (negative electrode active material) was pulverized and classified so that the average particle size was about 20 μm.

  Next, 100 parts by mass of flaky artificial graphite was mixed with 3 parts by mass of styrene butadiene rubber (binder) and 100 parts by mass of an aqueous solution containing 1% by mass of carboxymethyl cellulose. This obtained the negative mix slurry.

  Subsequently, this negative electrode mixture slurry was applied onto both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm and dried, and the obtained electrode plate was rolled. As a result, a negative electrode plate having a thickness of 0.156 mm was obtained. This negative electrode plate was heat-treated with hot air at 190 ° C. for 8 hours in a nitrogen atmosphere. The negative electrode plate after the heat treatment was cut to obtain a negative electrode having a thickness of 0.156 mm, a width of 58.5 mm, and a length of 750 mm. In addition, the negative electrode active material which exists in the part (edge part in the longitudinal direction of a negative electrode) which does not oppose a positive electrode active material when forming an electrode group was removed.

  Then, an N-methyl-2-pyrrolidone solution (concentration 8% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 97: 3 (mass ratio) was applied on the surface of the negative electrode and dried. . Thereby, a negative electrode side polymer layer having a thickness of 1 μm was formed. Thereafter, a dimethyl carbonate solution (concentration of 5% by mass) containing a polymer copolymerized at a ratio of VDF: HFP = 85: 15 (mass ratio) was applied onto the surface of the negative electrode polymer layer and dried. Thereby, a main layer side polymer layer having a thickness of 1 μm was formed.

  Then, a lithium film having a thickness of 100 μm, a width of 50 mm, and a length of 50 mm was pasted on the end portion (portion where the copper foil was exposed) in the longitudinal direction of the negative electrode.

(Battery 12)
A battery 12 was produced according to the same method as the battery 11 except that the negative electrode was produced without attaching the lithium film to the copper foil.

(Battery 13)
A battery 13 was produced in the same manner as the battery 11 except that the polymer layer was not formed on the surface of the negative electrode plate.

2. Evaluation Method Using the same evaluation method as the evaluation method in Example 1, the batteries 11 to 13 were evaluated. Here, in this example, the charge end voltage was 4.2 V and the discharge end voltage was 2.5 V in the charge / discharge cycle. The evaluation results are shown in FIG.

  In this example, the capacity of the battery was measured. The battery has a capacity of 25 ° C. with a constant current of 1.4 A until the voltage reaches 4.2 V, and after charging with a constant voltage of 4.2 V until the current reaches 50 mA, the battery capacity is 0 The capacity when discharging is performed until the voltage reaches 2.5 V at a constant current of .56 A.

[Discussion]
The result of Examples 1-3 is considered based on FIGS.

Example 1
In batteries 1 to 4, the defect rate after 48 hours after assembly and the defect rate after 500 cycles were both zero. When these batteries were disassembled and the respective cross sections of the negative electrode, the negative electrode side polymer layer, and the main layer side polymer layer were observed, precipitates of metal elements such as Fe or Ni were observed in part. However, these precipitates did not reach the positive electrode beyond the separator, but were formed along the surface of the negative electrode.

  On the other hand, when a battery in which an internal short circuit occurred among the batteries 5 to 7 was analyzed in the same manner, a metal element such as Fe or Ni was deposited in a needle shape, and the deposit penetrated the separator and reached the positive electrode. .

  In each of the batteries 1 to 4 and the batteries 5 to 7, the total number of moles of metals present in the polyethylene film, the negative electrode side polymer layer, the main layer side polymer layer, and the electrolyte solution was quantified by ICP analysis. The number of moles was almost the same in batteries 1-7. That is, the amount of dissolved metal foreign matter was the same in the batteries 1 to 4 and the batteries 5 to 7. However, since the deposit shape of the metal foreign matter was different between the batteries 1 to 4 and the batteries 5 to 7, no internal short circuit occurred in the batteries 1 to 4, whereas an internal short circuit occurred in the batteries 5 to 7.

-Example 2-
The same result as in Example 1 was obtained.

Example 3
The discharge capacity of the battery 12 was smaller than the discharge capacities of the battery 11 and the battery 13. The reason is that the irreversible capacity is not compensated for the negative electrode.

  In the battery 13, since the negative electrode side polymer layer and the main layer side polymer layer are not formed, needle-like precipitates penetrate the separator and reach the positive electrode as in the batteries 5 to 7 and the battery 10, As a result, an internal short circuit occurred.

  As described above, the present invention is useful, for example, as a power source for consumer equipment, a power source mounted in an automobile, or a power source for a large tool.

1 Battery case
2 Sealing plate
3 Gasket
4 Positive electrode
4A cathode current collector
4B cathode mix layer
5 Negative electrode
5A negative electrode current collector
5B Negative electrode active material layer
6 Separator
6A Main layer
6B 1st thin film
6C second thin film
7a Upper insulation plate
7b Lower insulation plate
8 electrode group

Claims (10)

A non-aqueous electrolyte secondary battery in which a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte are housed in a battery case,
The separator has a main layer and a plurality of thin films,
Each of the plurality of thin films has a smaller film thickness than the main layer, and has a smaller ion permeability than the main layer,
The plurality of thin films are non-aqueous electrolyte secondary batteries having different ion transmittances. The nonaqueous electrolyte secondary battery according to claim 1,
The thin film having the smallest ion permeability among the plurality of thin films is a non-aqueous electrolyte secondary battery provided on the surface of the negative electrode. The nonaqueous electrolyte secondary battery according to claim 2,
The thin film having the smallest ion permeability among the plurality of thin films is a non-aqueous electrolyte secondary battery bonded on the surface of the negative electrode. The nonaqueous electrolyte secondary battery according to claim 1,
The non-aqueous electrolyte secondary battery in which the plurality of thin films are arranged such that the ion permeability decreases from the positive electrode toward the negative electrode. The nonaqueous electrolyte secondary battery according to claim 4,
The main layer is provided on a surface of the positive electrode;
The thin film having the highest ion permeability among the plurality of thin films is a non-aqueous electrolyte secondary battery integrated with the main layer. The nonaqueous electrolyte secondary battery according to claim 1,
The plurality of thin films have different hexafluoropropylene concentrations,
A thin film having a low hexafluoropropylene concentration is a non-aqueous electrolyte secondary battery having a smaller ion permeability than a thin film having a high hexafluoropropylene concentration. The nonaqueous electrolyte secondary battery according to claim 6,
Each of the plurality of thin films is a non-aqueous electrolyte secondary battery including a copolymer of hexafluoropropylene and vinylidene fluoride. The nonaqueous electrolyte secondary battery according to claim 6,
The thin film having the smallest ion permeability among the plurality of thin films does not contain hexafluoropropylene and is a non-aqueous electrolyte secondary battery made of polyvinylidene fluoride. The nonaqueous electrolyte secondary battery according to claim 1,
The positive electrode has a composite oxide containing lithium, a first metal that is a metal other than lithium and oxygen, and
When the total number of moles of lithium in the positive electrode and the negative electrode is x [mol] and the total number of moles of the first metal in the composite oxide is y [mol], x / y is 1.05 or more. Large non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 9,
The non-aqueous electrolyte secondary battery in which the negative electrode has silicon, tin, or a compound containing silicon or tin.

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